I'm not upset by the fact that Mercer is going to voice Minsc. I think he actually does a decent job of it.
That said, I have a like/hate relationship with Mercer and Critical Role. Veteran TTRPG players obviously recognize that CR is a performance and not a 'real' campaign, but over the last few years we've seen the popularity of D&D skyrocket for a variety of reasons (Critical Role, Stranger Things, Big Bang Theory, the plandemic, etc.) and a significant portion of new players that come into the game believe that D&D is really played like the performance they see on CR. I've dealt with the misconception personally. I won't lie and say I didn't enjoy some of CRs campaign 2 for what it is, but I'm not a die-hard fan. However, CR did attract a huge, die-hard crowd of mentally-ill 'theater kids' types with rainbow hair, believe women can have dicks, and have pronouns in their bios. That portion CRs fanbase is the loudest and most supportive of CR despite the fact that A LOT of those sycophants don't (and won't) play the game. They woke mob has made CR enormously successful and all the other D&D streamers are scrambling to reproduce their success, but to even have a chance to capture their share of the cult they have to continue normalize the degeneracy and pander to the cult.
In fact, I cannot think of a single D&D stream that doesn't feature 1 (or more) trans players and multiple people that are either non-binary and/or part of the LGBTQLMNOPBBQ+ group. How do individuals that comprise tiny portions of the overall population end up in every game unless the players are being curated to ensure they're "on message."
TL;DR Fuck Mercer being in BGIII because it adds more fuel to the normalization of the Leftist clownworld.