I write a lot on Quora and respectfully disagree with OP here.

I like the fact that I can delete my questions or answers from time to time.

It's my content. Not the Internet's.

If I change my mind about something I wrote, I want to be able to edit it and delete it.

Some of my best answers are ones I edited many times over time. I use Quora and its readers to help me improve and correct my answers. The first draft is often not that great. Quora reduces the risk for me to submit my answer and post it.

I understand there are other sites where my content would be more public and permanent and I share on there too. But I often write and re-write on Quora before sharing my content to other sites.