I agree with what you say about passion vs. irony. It's weird how, in a society that allegedly prides itself on "acceptance" and letting people "be who they are", publicly showing passion about almost anything but politics or money is considered a really bad faux pas. Maybe it's insecurity. After all, caring about something usually means being vulnerable about that thing as well. I'm not convinced that's all it is, but one of the purposes of irony does seem to be serving as a shield (at least in my experience, I used to shield myself in bitter irony a lot).
I'm not sure we have a good idea of what "acceptance" actually is. Instead, we're just mouthing the platitude that we accept people for who they are, when that's demonstrably not the case.
Irony is absolutely a shield, especially online where criticism is the default method of communication.