I think the distinction is that the 'cake maker' could not be compelled to use is 'artistical craft' for purposes he didn't want to.
i.e. if it was an off-the-shelf cake, there would have been legal problems.
But a 'song writer' I think can't be compelled to write a song in such circumstances.
It's a little bit of a digression though:
For networking - most people agree in total neutrality i.e. AT&T cannot inspect our packets for 'bad words'.
On the other end, for Social Networks, we mostly agree they should probably have the right to moderate on some level according to their own rules. Perhaps we could require some consistency and objectivity or something, but generally speaking, I think we can live with Section 230 there.
The 'big issue' in IT I think has to do with hosting, which is a service one might deem should be 'neutral' - at the same time, companies may not want to host certain content and may be able to demonstrate 'harm' by doing so.
Like Amazon dumping Parler as the threshold / test case, along with this GoDaddy example - which is complicated because on one hand it's 'expression' on the other, there were some very serious and probably illegal things going on there.
In tech, we tend to focus on these social issues, but imagine if 'Brick and Mortar' business started doing this? i.e. UPS refusing to deliver packages? Or the 'Paper Company' refusing to sell inkject cartridges?
For commonly available things, like groceries, probably we can allow discrimination, because after all, someone can just go down the street to the next one, but for products and services which are unique, it really poses a problem.
However much we might not like some groups, we have to be really careful about banning things.