Which philosophers have defended both the claim that any attitude (a pro attitude to anything) can ground meaning and moral error theory? It may even be the the received view among the population in general.
There are indeed some philosophers who think that any pro attitude toward anything suffices for meaning
One is not really being true to oneself, losing oneself in a meaningful way, or having a genuine reason to live insofar as one, say, successfully maintains 3,732 hairs on one’s head (Taylor 1992, 36), cultivates one’s prowess at long-distance spitting (Wolf 2010, 104), collects a big ball of string (Wolf 2010, 104), or, well, eats one’s own excrement (Wielenberg 2005, 22)... there seem to be certain actions, relationships, and states that are objectively valuable (but see Evers 2017, 30–32) and toward which one’s pro-attitudes ought to be oriented, if meaning is to accrue...[philosophers] usually seek to avoid the counterexamples, lest they have to bite the bullet by accepting the meaningfulness of maintaining 3,732 hairs on one’s head and all the rest (for some who do, see Svensson 2017, 54–55; Belliotti 2019, 181–83).
And if nothing is moral then that might open the floodgates even further, so that not only is maintaining an exact number of hairs meaningful, but that no steps we take to do so (headhunting) are morally wrong.
Who could defend such a claim? To say that anything can be meaningful and no way of getting it is wrong seems like the antithesis of philosophy.
Or are the two are actually incompatible, so that if we take error theory seriously enough subjectivism can be limited and exclude silly (if not evil) counter examples.