I disagree 100% with you on this. You have good points but those very points are the very reason why I'm for deletion and against data retention.
"And honestly, I would much rather you not contribute to a conversation if you are going to come around later asking for your part to be deleted." That statement perfectly describes what's wrong with the silicon valley "dataphile" era. You're encouraging the shutting down of conversations, not the growth of more.
Even Y-Combinator said it in interviews that founders reveal more during more intimate interviews and talks than ones on camera. When you go around with a microphone and camera and record and set into stone what people say it doesn't encourage them to say more, but rather less. Because they're not sure if that information can be used against them in the future. When you fail to give users privacy and data retention rights they may just run away from your platform altogether.
There's a dread a user feels when they realize they don't remember what they said or who they were 10 years ago, but the whole internet does.
1) I don't mean this as an insult but what is your age? Because when I was younger my views matched yours, as I grew older the mental stress of my digital self being all over the place began to build up. It's something that happens with time and age. Sure there are outliers but for the most part we all slowly tun into privacy advocates as we get older.
2) "When you go on a redact and purge, you are destroying something that not just that you created, but something that tons of other people took part in"
It's better to create and delete rather than to never have created at all. Also, we're talking about Twitter, Facebook, Hacker News, and blog comments. This isn't a scientific journal, National Geographic, a Newspaper, or a text-book. We're talking about internet comments here. There's a time and place for data retention and I don't believe this is it. The burden of feeling like your life is cataloged on the internet with you having no control over it. The burden of feeling like your identity is split up in a million different little pieces is not a feeling you want your users to feel. No facebook or twitter or HN post is worth undermining basic user rights of privacy and deletion.
3) Your views on data retention seem extreme to me, the very conversations you're trying to permanently save will in a few months become outdated, no longer visited, not important, and useless. So what if someone deletes a comment and people reading 5 years in the future don't see it. What is the importance or significance of it that makes it worth destroying user rights. This is a sort of "Data Pack-Rat mentality", an obsession with archiving and compiling everything that everyone has ever said into a perfect neat little collection. And anyone that gets in the way of that perfect collection is a threat to it. You're more sympathetic and caring toward "the collection" than the users who create those collections.
I'll agree to disagree with you. I can't and don't want to change you but at least now you know why I am the way I am. Who you were 5, 10, 15, 20 years ago is not who you are now. What you care about changes, what you think changes, your identity changes, your dreams change, and unfortunately comments do not.
I believe User rights are more important than a perfect archive of some internet comments on a website.