To be clear, when I say "occasionally" here I'm talking about attendance for non worship purposes, passively attending for a wedding or funeral or what have you. I definitely agree that if you thought it was an appropriate place to worship, you'd for all intents and purposes fall under the Indult label.
I think ultimately the issue doesn't predominately come down to liberalization pre Vatican II, Sede vs non sede, or most of the other things that people are making this about.
I think it ultimately comes down to whether the NO is a Satanic parody of Christ's sacrifice vs if its simply a Protestantized service.
*Perhaps I am ignorant on some level.* I was never an NO Catholic. But from everything I'm aware, the changes were *predominately* designed to make the Mass look more like Cramner's Mass. You've got the communion in the hand, you've got the table replacing the altar, versus populum, deemphasis at least in many cases on the sacrificial character of the mass, etc. Oftentimes cheesy music. Honestly things that remind me of my time in Protestantism. Given that assumption i think the same principles regarding attendance would apply for a Protestant service. I think you could go for a wedding, but you wouldn't commune there.
However, some here seem to think that its more of a Satanic blasphemy than equivalent to a Protestant service. If that's the case than I'm ignorant, but also if that's the case I'd agree with not attending, not even for a wedding or funeral. I couldn't in good conscience "passively attend" a black mass, and I'm not aware of the church ever allowing that (as it has allowed passively attending Protestant churches.)
If its inherently evil to go, then you shouldn't go. The issue is whether the thing itself is a Satanic blasphemy that needs to be avoided at any and all costs (like a black mass) or if its more like a Protestant service (the thing itself is wrong but the Church lets you go for certain social reasons.)
This is ultimately what the debate comes down to IMO.