For anyone who thinks that the parent comment refers to the Colorado baker case (https://apnews.com/article/130137ace2e8416aa207456827fae92b), note that the baker did not refuse gay customers per se, but refused to customize cakes that celebrated gay marriage: gay customers could still buy non-customized cakes.

For anyone who thinks the above is too minor of a distinction, a potentially worthwhile question to explore would be whether, for example, an African-American baker (who customizes cakes) should be allowed to deny a customer's request to celebrate religiously motivated white supremacy.

Personally, under current law, I think Apple and Google should be able to determine whether an app like Parler is allowed on their platforms, although I think that concentration of power (whether in a corporation or in a government) is generally not good for society. I also think that there should be some base level of services (e.g. ISP) that should be treated as a utility (e.g. we don't deny someone water service because of his bigoted opinions).