This feels like a bit of a staw man argument, I'm not sure there's any reason to read into it that you could help someone do morally bad things and feel good about it.
To be clear though feeling good is not the justification per se, it's pretty much just the signal that you're aligned correctly. When you aim outward, morality becomes less about self image and more about stewardship which is why it tends to work.
I’m also not claiming morality is relative or "attained" particularly beyond normal development as an adult. I would assert that we already know what’s right, the problem isn’t discovering the moral law, it’s obsessing over our own righteousness instead of living it.
Presumably you imply that moral righteousness, too, is best attained intuitively, by being useful to others and helping them (to do whatever, like a useful idiot?) without conscious thought for what's right.
Or else you're saying "help people for no reason even though it isn't right, and you'll end up feeling good that way so it's fine".