Sometimes when I enter a venue and there's a set right in front of me, I can just jump straight in. But most of the time that's not the case.
When a set is not right in front of you and there's a bunch of people spanning the distance between you two, how do you justify (implicitly or explicitly) approaching the set?
The point of things like opinion openers is so that they don't think you're hitting on them. But "just happening" to stop and think of this question while walking past the set is about as subtle as a flying brick.
This isn't theoretical. I've gotten reactions like, "Why did you ask us?" "Are you asking everyone else?" And of course any guys in the set never warm up to me because they know what's up.