It's not really something you can ban, because it's an obvious source of conflict that a show like The Simpsons should explore. There have been many fine episodes that have done just that. However, they have gone to the well so many times that they're bringing up dirt and sludge off the bottom, so in that regard, I am in favour of them taking a break from what has become an overused plot.
Beyond overuse, the current characterisation doesn't allow marriage crisis plots to resonate the same way they used to. In the classic era, Homer and Marge's marriage was portrayed as a generally (and genuinely) good and healthy one, albeit not immune to conflict and rough patches. This was important as it allowed the episodes to resonate emotionally despite the fact you knew the status quo would be preserved by the end of the tale. Such episodes would use their conflict to demonstrate how a relationship could be affected and tested by various factors - three young kids including a troublemaker, money problems, ennui, feeling underappreciated, etc - but also ably prove that Marge and Homer's marriage was strong enough to overcome those hurdles.
Conversely, later episodes have portrayed their marriage as an unhealthy one that's hanging on by a thread. On top of being far more depressing, it means that maintaining the status quo is unearned. Whatever the problem is, it'll be glossed over in a way that suggests nothing is really fixed and we shouldn't really celebrate this, and the only reason we're at this point is because the show is maintaining the status quo. As a result, there are no emotional stakes, nothing that makes you care and distracts you from the obvious result of the episode's resolution. It's an unearned happy ending that doesn't even feel all that happy given the context.
Marriage crisis plots in the classic era also did a better job of setting up the conflict, whereas post-classic marriage crisis plots have felt contrived. Of course, this could be said of a lot of plots in general when comparing classic and post-classic episodes, but there's a particular quirk to marriage crisis plots. In the classic era, the story flowed into them more organically. Take "Secrets of a Successful Marriage", for example. Homer's inadequacy after he's made to feel stupid leads him to adult education, where he's instead inspired to teach a class to prove he's smarter than people think. An offhand remark leads to him teaching a class on marriage and relationships, and after failing miserably, he inadvertently becomes a hit because the class decides they're more interested in the gossip he's let slip. It strokes his ego, which had been hurt in the opening scenes of the episode, and so he continues to betray Marge's trust by telling the class secrets. The resolution may seem a bit rushed, but it's part of the humour and there's still a sweetness to it. The reconciliation is simple, but it makes sense given the conflict and how it came about.
Moreover, there's a flow to it: a logical path of events that leads to the conflict where someone (usually Homer) is clearly in the wrong, but also sympathetic. Other episodes centred on Marge and Homer's marriage in the classic era have a similar flow, often involving mundane events that nevertheless can prove to be a speed bump in a relationship. They're grounded in down to earth concepts, like feeling neglected on your birthday or embarrassed because your significant other harshly scolded you in public, meeting someone attractive that you have a lot in common with when you're already in a committed relationship, getting drunk and obnoxious at a gathering, and so on. Those stories are set up well from the beginning, have their funny moments along the way (such as Homer's bumbling attempts to reconcile with Marge and Reverend Lovejoy's blunt advice in the aforementioned "Secrets of a Successful Marriage"), both Homer and Marge remain sympathetic and likeable in the conflict, and the resolution is based on the strength of their relationship. The results are strong stories that as I said, resonate emotionally even though you know what the ending is going to be.
Compare this to later episodes that suddenly change gears with an unrelated story turning into (yet another) marriage crisis plot; one that feels shoehorned in as the main conflict in an episode that had a much fresher and more interesting story going on before that. Sure, an episode like "Secrets of a Successful Marriage" may have taken a long walk to get to the marriage conflict, but it was a story that logically progressed to that point with understandable actions and motivations. The worst marriage crisis episodes begin with a story that suddenly takes a left turn into Marge being upset with Homer, followed by an equally contrived resolution that doesn't feel earned. Once again, the fact that their marriage is portrayed as hanging by a thread is a big problem here, as the already shoehorned plot isn't about how a strong marriage overcomes challenges, but how a bad one survives a little longer because it has to for the status quo. It's sloppy, emotionally-deficient writing, and it leads to dismal, repetitive episodes.
When considering the freshness of marriage crisis episodes and the way such a conflict used to be tackled, I'd like to throw an interesting example out there. "The Mysterious Voyage of Homer" is a divisive episode (I personally love it), but it has a really interesting take on a marriage crisis plot. It starts out as you'd expect, with the Chilli Cook-Off inviting Homer to make a fool out of himself and Marge once again. You think it's heading in that direction, but instead Homer keeps his word not to drink, and it's through misunderstanding and gossip that Marge thinks he broke his promise, when in fact Homer going off the deep end is the result of Chief Wiggum's vengeful machinations. Instead of trying to win her back through the rest of the episode, it's Homer who is questioning the relationship, as during his trip, insecurities about his marriage bubble to the surface and he's left wondering if they're really a good match, really soulmates. It's unusually but refreshingly introspective for him, and although Marge isn't unsympathetic in the episode after being led astray by Helen Lovejoy's toxic (and false) gossip, you can understand why Homer is pondering the question. Normal sitcom tropes would portray him as being ridiculous for even considering it, but after a fight where Marge doesn't believe him when he's being truthful and he's not sure she gets him, it's understandable and interesting that Homer - normally portrayed as the "lesser" person in the couple who should be thankful they're with the other person - is the one doing the reflecting. Also, Johnny Cash as the Space Coyote is awesome, and brings levity to the episode.
With all that in mind, I do think the show should avoid marriage crisis plots unless they have a really good story that can portray Marge and Homer's marriage as one that's strong enough to overcome the obstacle, and for that matter, worthy of overcoming that obstacle. Even then, I think they've run the idea into the ground so much that I'd be perfectly fine if they never touched on that plot again, or certainly kept it to a minimum. You can't outright ban it because it's such a fundamental plot device, but if you don't have any good stories to tell with that particular conflict - and frankly, they really haven't in quite a long time - then at the very least, put it on ice for a while.