This is a long reply, so TL;DR redditors are idiots and the two situations are fundamentally different.
The problem with the comparison is that it starts from the assumption providing a platform on the internet is essentially the same as baking a cake. Once you've granted that, the logic of the principle suggests either banning conservatives is wrong or it's okay not to bake personalized cakes for perverted functions. But it is far from clear they are the same. And if they gave fundamental differences, then application of a principle may very well yield different results.
The trick in antitrust law is defining the market. When Office Max and Staples wanted to merge, they argued the market was a broad one representing every place people could or did shop for office supplies. So it included Walmart, Amazon and lots of other places. Therefore the merger would not grant them monopoly power. The government disagreed, said the market was simply for office supply superstores, and blocked the merger. Staples then went bankrupt so the supposed "competition" to benefit consumers the government was trying to preserve was lost anyway.
The thing about youtube, reddit, etc, is that they are supplying an infrastructure. They are not crafting the messages of their users. They also initially hold themselves out as platforms for everyone before they start their censorship.
Contrast that to a baker (which is a form of artistry) who is not in the business of giving the public access to his kitchen to make their own cakes. He is in the business of physically himself creating a form of edible artwork. The complaint has never been that he won't sell food to faggots. It's that he won't personally craft an expressive product with a message he finds repugnant.
Youtube banning conservatives and a baker refusing to make a faggot's wedding cake are simply nowhere close to analogous. So the principle which the redditors think is so clever just doesn't apply the way they want.
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