This is accurate. More often than not, trying to do something good for others will end up making you feel like an idiot. For the person on the receiving end, you are a jackpot. Instead of being shown gratitude, you're likely to be exploited.

But then again, would it really be a genuine gesture on the giver's end if they were to filter based on the receiver's character or whether they will be grateful for it?

The positivity from you is likely to be absorbed by the negativity, never to be seen again, instead of snowballing into a boulder of positivity as you'd hoped. I feel the only answer is to be an endless source of positivity. In that case you're not worried whether the drops of positivity from you end up somewhere they're appreciated or not. The negativity sponges might suck you dry, so it's not for everyone. For most of us the answer might be to constrain our positivity outlets into safer, more controllable spaces (volunteering for an organization, etc.) where it is less likely that we might feel anything negative for our efforts.