Lyrics seem to have the strongest safeguards out of everything. (Try it! On some APIs, you might see moderation/refusal behavior you don't see with anything else, even cyber)
On top of this, you would want an expirable proof of humanity to reduce account takeover as a security vector and publicly sharing failed proof attempts would quickly deter actors from targeting projects en masse.
That is why you must think carefully who you vouch for. Like in a house party. If you bring someone who does not act well, it reflects bad on you.
Ultimately, a shrinking contributor pool is the inevitable consequence of code generation being virtually free.
How many people do you envision the average person vouching for? If it's less than 3, that's a problem.
Anything illegal, for that matter. Crime as proof of humanity. Fun future!