You've demonstrated that there are numerous potential downsides to Reddit. (Though really all of the hinge upon someone not taking the time to "cultivate" their inputs correctly.)

What you really haven't demonstrated is that these downsides overcome the positives and create a "net bad" for society.

I have absolutely no idea how to convince you to change your view because your entire view appears to be self-centered. Self-centered in that what I hear when reading your post is a very personal set of experiences and frustrations. I, literally, do not see the same Reddit you do:

My experience in /r/askscience is not as you describe.

I have never subscribed to the front page or /r/funny.

I give and receive practical, relevant, and useful advise in /r/bikewrench and /r/photography.

I lost a significant amount of weight and gained a significant amount of strength using the appropriate subs.

I've seen people talked out of suicide.

I've seen far flung people find common ground.

Are there broken people acting out in broken ways? Sure, in every sub I work in. They're easy to filter out, though. And if a sub gets "sick" or in other words dominated by broken people or broken groupthink it's easy enough to cut off the offending limb and grow another one.

But back to my point. I hear a tale of woe and personal experience. What I do not hear is any reasonable explanation for how Reddit is a net bad. If you want to be convinced to change your view IMHO you need to actually defend it, not just shit on some things which exist everywhere (read the discussions on wikipedia if you don't believe me) and which most people filter out.