The "warm glow" is a good way to describe it. I've tried to liken zapping to tossing some money in a street musician's hat: it's a donation but also a payment. It's not exactly charity, but it's also not required.

I probably should have included something about how most payments on SN are not required (the only required payments are posting fees, and even those aren't fully required).

It's interesting to compare my feelings about payments on SN to my resistance to paying for X. I still can't bring myself to shell out the $8 a month or whatever it is. Whereas if they just charged me a few sats to post and paying that fee kept my posts on equal footing in their algorithm...