Well, engineers can have a lot of ethical responsibility. A resume that show you have no scruples doing unethical things is a fine way to gauge if someone is a suitable match.
Not much different then background checks for working in schools or what ever.
If a founder or person in charge of hiring views a candidate as a threat to either the business or their customers then they have every right to pass on that candidate.
Which is something people do. For example, you wouldn't hire someone who takes their politics to just-under-violent extremist levels, as it would be bad PR.
Not much different then background checks for working in schools or what ever.