I'm starting to notice some of this behavior too. Multiple players over the last few days request to blacklist a card. Usually they just resign and move on when I deny that request, but I had one player get abusive with me last night. They requested I not play with Rebuild, and resigned before I even had a chance to reply under the assumption I'd just be cool with a re-roll like they said they wanted if I wouldn't agree not to use the card. I left the table because I'm a pretty firm believer in learning to play with all the cards and that if special rules are needed then those players can play non-rated games.
I played another game with a different opponent via automatch then got paired with this player a second time via automatch and decided to go ahead and play it out. They started questioning me why I left and I said "I am not into 'blacklisting' cards." They then proceeded to send 2 or 3 messages with no response from me justifying why they didn't want to play with that card. I said "I have cards I hate too, but I play what I'm dealt," and I think near that point I also said I wasn't feeling like arguing about it. They then started accusing me of being mad over a game, being unable to play it for fun, and being different from "all the other players" that apparently let them do this a lot.
I told this player they were being pushy with me, but they continued to keep messaging me through the end of the game. I told them I would blacklist them and I have, but it would be really nice to have some sort of reporting function so that we can alert the admin to users who are asking for special accommodations over pet cards they hate. I don't mind the asking so much, but being badgered over refusing is unacceptable. Seems like the OP has also been punished for simply saying no and it would be nice to avoid those kinds of characters and personalities on this game platform if possible.
The user in question for me was Durgle, in case the OP wants to pre-block that user too.