People just delete their accounts and all the messages are deleted. Plus Reddit posts transparency reports every year. Here is 2016: https://www.reddit.com/r/announcements/comments/63974m/its_that_time_of_year_again_we_just_published_our/ .

And another bonus: on Reddit only the administrators can see your IP. And trust me they are too dumb (google spez CSS, he basically didnt know too well what he was talking about) to go into the trouble of deleting specific posts. On 4chan a random janitor that doesnt even get paid can see (and possibly leak) your IP.

Dont get me wrong I do enjoy both sites, but for privacy reasons I would rather use reddit and delete my account after one or two months. And they dont care if you post behind a random VPN or using TOR nor you are forced to pay extra for that (lets be honest, you shouldnt pay extra anyways).
Inb4 reddit shill, go back to reddit, etc.