Older post I know, but I found a solution that works for me I'd like to share.
I simply bring my own portable toilet with me. I use the Luggable Loo ($50 at CT) and the Double Doodie bags ($20 for 6). This way I always have my own private toilet (with no worries about unsanitary past users), I don't leave any unsightly mess behind, and I have zero impact on the mountain environment (I simply deposit the bag in the trash).
Minimal cost for a peace of mind.
Adams