I would draw the line when self voting is no longer necessary to launch undervalued posts in order to attain a "seed" audience.

Other words, when it reduces opportunity for supporters, when they are already on the hook to share in a reasonable % of the reward.

Many shrewd authors know that most curators are not aware that the reward pool can be and has been devalued for them.

I'd say it's another microcosm of what we see in the world all around us.

A gray area.. I think so - in that perception of need vs. greed.
"Gray area" is expected when there is a lack of structured boundaries but I don't think that these are necessary and may do more harm than good. Difference in opinion are healthy to a great extent provided these are not allowed to assume power over the choices of others.

By bringing it up in conversation however, if there are many actual human beings at the table- raises awareness and with that, a chance to shift additional weight toward communal benefit and growth.