Are you intentionally ignoring the fact that from day one a user had the right to edit by adding to or subtracting any part of their content or to delete the entire comment? How is this vandalization? This is user control, the same level of control granted on a site that was built for users to post on and discuss any subject - free speech was a keystone principle until some bad actors couldn't stop posting trash and ended up rightly banned.
Millions, maybe billions of comments are digital dust at this point. Like thoughts lost just before they made it past the tip of your tongue. This is normal and expected behavior. Conversations get lost in the fog.
Reddit isn't a Banksy. Today, it's more like the monkey area of the zoo in spots with each monkey's hand ready to sling the shit. When you consider the huge number of bots on the site it is likely worse than that.
Originally /u/spez and /u/n0thing set a standard where a poster who dropped a reply containing information that didn't fit the established narrative and tried framing it as an accurate answer was asked to post the references that supported their conclusion. It was "tits or get the fuck out" days. That by itself promoted healthy discussions and worked to disseminate accurate information on important topics. It helped establish a cadre of users who are outstanding in their fields and who enjoy sharing their expertise with others.
In time, especially after Digg imploded themselves, the expansion of subreddits made it untenable for proper moderation so a lot of boogers were allowed out of the nostrils and while the quality of discussions in general on the site was still good, many subreddits were established where people could say anything with no one calling them out. It sideloaded all the horseshit that used to hit the front (and only) page of reddit to the subs - stuff like goatse, nsfw content, etc. In the earliest incarnation reddit's front page was a minefield of stuff you really needed to avoid if you wanted to surf online and still keep your job. Early users learned fast to read the comments before opening the post.
I'm having a hard time understanding how a feature - user control of content they post - is mislabeled in your reply as vandalism when the user elects to employ that feature in managing their content.