trying to stop your spouse from engaging in a recreational activity they enjoy is controlling behavior and not okay.
So much this!
Unless one's partner's downtime activity is dangerous or illegal – murder for thrills, recreational bomb-making, basement meth production for pin money, crashing cars into things for jollies, etc. – one puts up and shuts up. There's some
minimal leeway for "immoral, in one's opinion," but as I wrote what feels like a million years ago: Getting into a committed relationship with someone without first learning their values, and either accepting those values or negotiating common ground with equal give and take on both sides of the table, is setting oneself up for failure. Revisiting the matter later on, when one should really know the other person (i.e., why the heck is it a surprise?), is closing the barn door after the horse has fled, joined a parade, and made its way to Mongolia.
Essentially, it comes down to a judgment on whether partner dancing writ large, or AT/Kizomba/Bachata specifically, are tantamount to infidelity. I would be shocked to see any significant number of the dancers here agree that it is.
I have met people who think that way. I can say with confidence that 100% of them were in a situation I'd characterize as: "My partner was interested in dance but I was not. When they did it without me, I felt left out, got jealous, and started trying to control them."
Whereas a solid 0% of them were in a situation I'd describe as: "My partner went off to dance without even trying to involve me. I felt sad that they didn't at least ask me to get involved, which made me worry about
why they didn't at least ask."
The "My partner likes to dance and I didn't know that when we met or bother to find out in the years that followed, so how could we have discussed the matter?" situation is mythical. It's a well-gas-lit mind game played by controlling people in order to justify being controlling.
And if it is not, then preventing a significant other from doing it is a serious red flag--and not only that, but quite likely to cause the marital problem that they are ostensibly trying to prevent.
Partner dance can certainly shine a spotlight on existing cracks in a relationship . . . it happened to me. But it doesn't
cause the cracks. As you wisely said,
preventing a partner from dancing causes cracks. Whenever I hear, "My partner wants to dance with other people and it's hurting our relationship, so I want them to stop!", it comes through as, "Our relationship has issues, my partner's dancing is shining a light on them, and I'm too craven to look at those cracks and fix them, so I want them to quit dancing and stop shining that damned light!"
Saving a relationship by ignoring its problems isn't possible. It's just putting off the inevitable. Living in ignorance isn't a whole lot more admirable than being controlling, and too often, one leads to the other.