What does that...what can that...possibly even mean, "that the character wouldn't"?
I think that here, and in subsequent posts, you have misunderstood
@hawkeyefan.
Hawkeyefan, in the post you quoted, was pointing out what he takes to be a tension between:
(i) the notion that social/emotional mechanics are bad, because they dictate that the PC does something other than what they "would" do (as conceived and authored by the player);
(ii) the notion that players will sometimes author PC responses other than what the PC themself would prefer (eg the player will sometimes have the PC make irrational decisions);
(iii) the player should have the same decision-making process and motivation as the PC, in order to preserve "alignment" between player and character.
This tension is only a problem if
the same person is advocating all 3 of these things: but it seems that some posters in this thread are doing just that!
@hawkeyefan has then suggested that - contrary to the assertions of those posters - the use of mechanics to help shape PC emotional/social responses is no more of a problem for (iii) than is (ii). And the sanity mechanic in CoC has been offered as a simple illustration of the point.
I will add something that I don't think
@hawkeyefan has, but that I suspect he may agree with (at least in a broad/general sense): If we use mechanics to sometimes establish or shape or constrain the PC's social/emotional response, then we actually do a
better job in relation to (iii) than if we rely on (ii) - because in the case that mechanics are used, the PC's social/emotional response is experienced
by the player as well as
by the PC as something that is not under the PC's control.