I wouldn't even work with him for 0% stake, as there is obviously a misalignment of values.

Treat business partners like you would dating. All I see is massive red flags:

"...to people who did not show any signs of being interested in holding such a discussion, for example at networking events."

"He takes every opportunity to rant (in strong language)"

Some doors should remain closed. I question the network and the people who would associate with such a person, those people would not be my target customers.