This argument boils down to X is good, therefore more of X is good. But you can see how that breaks down with even trivial examples. Not a great argument.

The second piece of this "a moral good is based on doing good outside of your own benefit" - says who? Why? This logic is also faulty. You're also cargo-cutting self-interest in here as a moral failure when many good things depend on humans acting in their own self interest. For example I completely and selfishly installed a new tree at my house. But the community benefits from carbon capture, shade, &c.

I understand the sentiment you have here and I think for everyday use and having some guiding principles it is probably fine, but don't confuse this for a principle that is actually examined. You can find contradictions rather easily, never mind solid arguments which expose cases where what you think is true is not really true and so forth.