If you're just talking donations, sure, it's definitely a great idea. Heck, MY business would accept donations of Bitcoins :)
But honestly, I just don't think the OP is worded well if that's the case. Being a liberty proponent doesn't really have to do in this situation, and I think the argument should be reworded to:
If you'd like the extra donations that Bitcoin users and supporters would be willing to spend/donate, then you should accept Bitcoin. By not accepting Bitcoin, you're missing out on a potential market.
The stuff about "true" liberty proponents and that misses the mark with me, because it reeks of judgement and force. Just my two cents.