As someone who was let go (contract didn't get renewed without any explanation or warning) for being trans, because the lady in charge of hiring and contracts was a bigot... I'm really not fond of this "don't fire people for being bigoted" argument.
People who go to Proud Boy meetings might know better than to say anything racist, sexist, etc at work... but they are still going to take those attitudes to work and interfere with the careers of marginalized people.
Would you rather a trans person or a TERF be out of a job? Pick one, there's no third option here.