I don't think that breaking them up is entirely necessary. Classifying them as public spaces in private ownership and extending similar freedoms from government to these large social media companies seems like a relatively reasonable approach. As to the counter argument that they are "private companies," corporations and companies exist because of the government. The positions allow for not only group ownership, but also for such limited liability that companies can collectively kill thousands and not be killed themselves. This can and should be offset by limited capability in scenarios where a corporation may have an unnatural leverage against competition.

I tend to be very libertarian leaning, but corporations are not individuals, nor are they held to the same standards, and as such shouldn't be allowed the same freedoms. Restricting business is natural, and civil rights laws have already made business owners do what they might otherwise not want to.

Extending freedom of speech rights enforcement to organizations with over 10m members or managing over 5b/year in revenue is not unreasonable. They already have platform protections.