I see a guy with blood stains on his gi and I think
1) It might be his blood. Maybe he bleeds too easy. I don't want his god-knows-what-infected blood on me. I'll roll with someone else.
2) It might be an old opponent's blood. Maybe he rolls too rough. I don't feel like bleeding tonight for someone I don't know. I'll roll with someone else.
Either way, I personally think it's disgusting. Bleach it, oxi clean it, peroxide it, whatever. Use a black marker to make it black like tar or oil. Just do something.
I wouldn't touch a girl's nasty period-stained underwear. I wouldn't touch an old bandaid on the floor. I sure as hell don't want to roll with no blood-stained gi.