There's ample for why it's illegal to discriminate against classes of people. Imagine business in the 20s with signs saying "Irish need not apply" or "No dogs or Jews". The recent case with the baker was extending the protection of human rights to gay couples.
Any "conservative" content that has been kicked off of platforms like YouTube has been specifically targeted not for political reasons but because they were spreading hate speech and/or dangerous disinformation. Things like racism, sexism, religious intolerance, specific accusations (ie Joe Scarborough is a murderer) or dangerous disinformation (ie 5G causes Coronavirus) are not intrinsic to any group of people. There's still plenty of content around mainstream conservatism that can be viewed freely.
I think any attempt to argue a slippery slope isn't valid. People aren't computers and just because you can't apply a mathematically rigorous distinction between these kinds of speech doesn't mean that a reasonable person can't easily distinguish them.