How can one avoid it without being in the kitchen and violating several other laws, Mojo?
Yes.
You’re oblivious, get it? Not avoiding the truth, there’s no reasonable way for you to know. You’re not doing anything to unknow. You’re ignorant, but not blissfully so. You go out, eat a deilcious cheeseburger and go home. No disease, no insult, no nothing.
I think we may be stumbling over some nits here. 
I’m being nitpicky about what “insult” or “harm” is, and others are insisting there could be disease. Or that they should somehow intuit the spit, it’s so awful.
Just thought of another analogy. It’s pretty ‘out there’, but here goes;
Suppose you’re a woman (or gay man) and you’re talking to a man who you find physically disgusting (ok, here we go), and this guy has an erection from talking to you? You don’t know it. Period. Same thing? Sure it is.
Sorry, couldn’t resist that one. One of them zen things.
Peace,
mangeorge
OK, but where are you going with this?
I really don’t know. I thought we were making analogies.