>this pair of arguments makes a very tempting motte-and-bailey. The left can make the more dramatic argument that “all billionaires are cheaters”. Then if anyone points out that it’s possible to inherit a billion dollars as a baby, before you could possibly have done anything wrong, they can fall back to saying “ah, but clearly the baby didn’t deserve that billion dollars, which is what I was talking about all along”.

This is not a "motte-and-bailey", as the fact that you can't "deserve that billion dollars" is already part of the original "pair of arguments". In a true motte-and-bailey the second argument is implied, here both are given out straight.

Also, “all billionaires are cheaters” trivially doesn't include the baby which merely inherited the money as having actively cheated. It does however trivially include the parent who amassed the amount as a cheater. And thus, it makes inheriting the amount inheriting the fruits of cheating.