If the content doesn't break a law and you make an editorial decision to remove it, then you have moved beyond the role of Common Carrier... that's the short-short-short version of the "this is the line that must be crossed" I've heard from legal experts in the past.
Being immune from prosecution and/or civil suit because you are simply the medium the information flows across is a huge thing. The protections come with huge strings, those primarily being that you don't make content-based or viewpoint-based moderation decisions. Your decisions to remove content are based on criteria that do not help or hinder any particular political or religious or (insert other component) here... but that do clearly prohibit material deemed against the law.
It's when you stray into prohibiting a particular topic of conversation when you get into danger. I sat and watched test Facebook Messenger conversations on people's phones disappear when they mentioned Hunter Biden and laptop in the same discussion. A conversation between two individuals, not posted to the world at large, disappeared. That was an example of a "subject that will not be discussed on this platform". That's a clear violation of the concept of Common Carrier protections.
If you don't want the protections of the Common Carrier concept, you don't have to pursue them. But if you do pursue them, that inherently means your platform will be carrying opinions you may disagree with.
The trap we've fallen into is not understanding the difference between "Hate Speech" and "Speech I Hate".