If you get denounced on a popular repo and everyone "inherits" that repo as a source of trust (e.g. think email providers - Google decides you are bad, good luck).
Couple with the fact that usually new contributors take some time to find their feet.
I've only been at this game (SWE) for ~10 years so not a long time. But I can tell you my first few contributions were clumsy and perhaps would have earned my a denouncement.
I'm not sure if I would have contributed to the AWS SDK, Sendgrid, Nunit, New Relic (easily my best experience) and my attempted contribution to Npgsql (easily my worst experience) would have definitely earned me a denouncement.
Concept is good, but I would omit the concept of denouncement entirely.