Without having read the law; in principle, it seems fair that if a company wants to create a public forum for open discussion then they should be obligated to keep it open (outside of speech that violates the 1st Amendment).
Now, that shouldn't mean that I couldn't go start a media platform tomorrow that panders only to conservatives. But I should be held to whatever standard I advertise my platform as being. It'd be like Parler, for example, marketing itself as a truly open platform that only removes 1st Amendment violations but shadowbanning liberal groups or individuals. (No idea if that happens or not, I'm not on any big social media except Reddit.)
So...in conclusion then, again noting I've not read the law, if Twitter or Facebook market themselves as public forums then they need to act like them. If not, let the blue banhammers fly...or, continue to let 'em fly, haha.