If I told you I was always a positive person, I would be lying. I tend to be negative at times, but it is almost always self-sabotage and not directed at others.
You are so right in commenting that doing or saying, or helping, other people brings us so much more to ourselves. In my previous job in a company, (now I am freelance yei!) unfortunately some people used to apply that saying that "they would rather be one-eyed to see someone else blind", a false Pyrrhic victory that somehow made them feel good?! I don't know, crazy things about human beings.
The truth is that I notice that there are people who find it very easy to "throw dirt" on others, they almost do it like breathing, it is part of their way of being.
I have felt the warmth in my chest, which brings to do something good for someone else and I think it is a beautiful feeling, although the other person does not always reciprocate, sometimes not even with a "thank you", but that is the magic of giving without expecting anything in return. To be left with the satisfaction that you did something well done and then hope that something happens like in the movie "Pay It Forward" which I hope you have seen. 😄
It can feel easier to apply negativity, to push one's own feeling of self-loathing, insignificance or poor self-worth onto others and think it's making one feel more powerful or valudated...it doesn't though, and when that initial rush of empowerment fades that individual is stuck within that miserable, hateful and despicable place they call themselves.
It's best to seek other solutions I think.