The mechanics in roleplaying games provide a shared language that is used to communicate what's in the imaginary space happening within our heads. That's it. I'm totally on board with mechanics "getting out of the way" and being unintrusive, but if they served no purpose and could be ignored we wouldn't have found a use for them. So, I don't see them as a necessary evil - I see mechanics as something that actually help. They are a tool, used to communicate vital information that keeps everyone on the same page. Doing away with mechanics completely basically makes the experience improv.
Second, from a personal perspective, I don't play roleplaying games because I want the purest roleplaying experience possible. If I wanted that, I'd do improv theater. I do it because I like games. I may not have a high tolerance for overly fiddly games, but I do enjoy rolling dice and figuring out how to work things out within the constraints of the mechanics. If that means having to use mechanical terms during play, as long as they aren't completely jarring and mesh well with the game it's a compromise that I think yields tangible benefits. Otherwise, using the mechanics while not talking mechanics just sweeps the thing that's making everything work under the rug. And this isn't even getting into the question of what is a mechanic anyway? If you've devised a system where you give hand signals every time your character uses a skill in order to avoid mechanics, you've just invented a mechanic.
In short, trying to not talk about the mechanics while using the mechanics is like roleplaying Fight Club (or saying that you don't need programmers for Salesforce).