So what?
There’s no law prohibiting these types of businesses from supporting a political candidate. They could plaster a huge “Vote For X” banner at the top of every person’s profile. Don’t like it? Don’t use it.
It’s not like Twitter is tax-exempt which would prohibit it from endorsing candidates like Churches.
Twitter is not tax-exempt but is certainly lawsuit-exempt to a large degree. The entire reason twitter has not be sued into oblivion for the actions of it's users is because of the protections Section 230[1] grants them.
But here is the pinch. Section 230 protection applies only as long as you act as platforms for 3rd party speech. But when they start plastering "Vote for X" banners on their websites of their own violations, they go from being platforms for 3rd party speech to 1st party publishers. That effectively removes the Section 230 protections twitter enjoys.
I much as I hate to say it, Trump might be right this once. Twitter has stopped being a neutral platform enforcing consistent policies for quite some time now.
[1]: https://en.wikipedia.org/wiki/Section_230_of_the_Communicati...
These companies have become, for many, infrastructural. For these companies (who also sell advertising) to take these kinds of actions would essentially be them bypassing campaign finance rules to give MASSIVE contributions of free advertising to candidates. I think its fair to argue that that would be unacceptable interference.
That's not at all how section 230 works. Section 230 protections. Section 230 provides protection from liability over what their users post. Whatever content they have of their own on their site is completely out of scope as far as section 230 goes.
But should it be illegal? IMO -- no. If this is the hill that some company wants to die on, let them try. Why not?
Thought experiment: If there was a political candidate running on a platform to destroy the internet, I think it would be perfectly reasonable for internet companies to vouch for the competition.