How much shit is safe to eat?

As far as sex goes, I don’t really think the question of safe/unsafe is really that helpful to ask. The better frame, I think, is risk.

All sex carries risk–hell, most every action we take in the world carries risk of one sort or the other. Scat is risky sex–risk of illness in particular–and it isn’t a question of *amount*, if anything it’s a question of who your partner’s are, what their current health situation is, and other possible risk/health factors like that. 

The only person who can determine how much risk you want to take on, and whether the complimentary reward/pleasure is great enough to carry it. I can’t make that judgement for you, and safety is bullshit anyway. What we mean when we talk about safety is lack of consequence, but the risk doesn’t go away.

The best advice I can give you is to be informed, talk about potential health risks with your partner(s), know that the risk is there, and own whatever decision you make.