Try just flipping the two parties in the original hypothetical - if you were an LGBTQ web designer and say Westboro Baptist wanted you to build a website for them, should you be required to build a website supporting their virulently homophobic message? Religion is a protected class, therefore you should not be allowed to refuse right?
Because that's what both the cake case and this case were about in essence - the line drawn is being required to engage in speech.
Since you didn't reply, I'll make my point clearer
We discriminate against hateful language all the time. Social media can't ban gay people just for celebrating a marriage. Because it's not hateful, despite what the Jordan Petersons of the world think
They CAN ban comments that homosexual people make if they say something like 'kill all heteros'
Due to anti-discrimination laws, social media companies are being forced to act this way. They might have some leeway to decide what is hateful, but there is still enforcement
These same laws apply to all businesses. So, for example, if a gay worker says, 'kill all heteros' to a customer, they might be investigated and get fired. This could even happen when just talking to other colleagues.
The message is the problem. The hatefulness is
And before you claim that the rules are the same for gay people, I want to note that most gay people don't say 'kill all heteros' specifically because they get punished any time they speak about minor stuff like 'it's better to be homo than hetero' as that is usually claimed as hate speech
Two last things
1) Stop pretending that hating gay people is a religious ideal. It's not. People claim it's a religious ideal because they want to be bigots without getting criticized. It's a smoke screen to bamboozle you. You're falling for it
2) Stop pretending that noting that gay people getting married is tantamount to a hate crime. It is beyond ridiculous