A few thoughts I've had in the past on the subjects of plastic mounts and weather sealing.
Wouldn't it be better during a fall that the mount actually broke?
and,
I don't subject my gear to harsh elements, weather sealing, or the lack there of, is not going to keep from or entice me into, buying a lens I want.
People love getting bent over this stuff, I find it funny when I read posts about these topics.