That’s pretty normal, we all do stupid shit as kids because of our environments/friend circles or just general growing pains.
Recognizing that what you’ve done is actually horrible is the most important step in terms of maturing and growing up, though of course it’s not the full battle. After all, how would someone change for the better if they don’t have such realization?
All in all you’re likely not a bad person, just someone who needs to/is in the process of maturing.
In a number-go-up kind of sense, yeah - it’s inherently gamification of social media and it is fun for some of our brains. However, I also think that karma or any other kind of “engagement accumulation” turns social media from a place of discussion into a competition for attention, where you’re more incentivized to post solely for upvotes. Only a small minority takes posting seriously like this I admit it, but it does make the experience worse for everyone.
That’s not to say the mindset doesn’t exist without karma, only that it gets amplified.