If you carry on the quote two more words:

> ... a nonexclusive

I.e. this section is talking to additional rights to the content you post to ALSO go to YC, not that YC is guaranteeing it (+friends) will be the only one to hold these rights or will enforce who else should hold the rights to your publicly shared content for you.

There's a more intricate conversation to be had with GDPR and public data on forums in general but that's wholly unrelated to what YC's legal page says and still unlikely to end up in an alarming result.

I think that's incorrect. Exclusivity would be something you grant to YC. These terms need to make sense to be valid. Claiming exclusive rights would mean they are forbidding YOU from licensing YOUR rights to anyone else.

Imagine Facebook claiming that by uploading images you are granting them exclusive usage rights to that image. It would mean you couldn't upload it to any other site with similar terms anymore.