"But if you like, say, IRON MAN, I think it’s likely that your reading enjoyment won’t somehow be forever ruined if Spider-Man were to guest-star in an issue." Not ruined forever but because I hate Iron Man, I'd rather not own an issue with that creep playing in it, so I skip them.

Anonymous
I think that’s perfectly reasonable: you’ve gauged what’s likely to detract from your enjoyment of a book, and then you avoid it. Doesn’t mean we’re going to stop putting Iron Man into books, of course, but you’ve sussed out what works for you, and you’ve got a plan that deals with it.