This is why if you are nice and polite to conservatives they start spouting more and more bigoted bullshit

I always interpret this as projecting their opinions. If you give the person nothing to suggest a specific political leaning and have a positive enough interaction it's too easy for them to assume you hold the same values as you.

I've honestly caught myself in the same, so I just try to stay apolitical in interactions at work until others reveal their opinions to me