I too hear this nonsense countless times.
I usually like to point out two things about this:
- that this "being imperfect" excuse is not compatible with the notion that someone is spirit directed. How could it ever be? If someone claims to be spirit directed and fails at providing truth, then what does this show?
- Is there any religion out there that couldn't make the same claim in order to excuse their failings? By what measure could anybody find out if a religion is true, if any failure could be simply excused by saying "we are imperfect?". You could point at catholics and call out their failings, and they could simply say "Well we are imperfect", or " Hey, we are waiting on God, he will straight things out"