I took mine out a long time ago...haven't cut 'em or put 'em back yet... headliner seems OK without it.I was considering doing the same as it interferes with my curtain, but part of it supports the shape of the headliner. The other option was to slice it off even with the steel panel.
I removed all four blocks of foam and replaced them with foam that worked with my interior. Below is a pic of that area in my mostly finished van conversion.Lump'o'styrofoam near the overhead bin...
I totally agree about not holding the airbag in. Tons of force as you say. I just think that the styrofoam is there to form a guide channel.My guess is they are there to cover the area and still easily come out when the airbags deploy. No way that thing holds the airbag in.