Can you elaborate on your point? Are you talking about Russian bot accounts, or that people in other countries may have views which are not suitable for Americans, or what exactly?
If your only rule for how to moderate your platform is "what is legal", how do you scale that out internationally where there are significantly varying standard for what legal speech is?
It's easy to point to 'oppressive' countries like China (where twitter is banned), or Turkey[1], or India[2] as examples of where speech can be severely limited, but there are many limitations to speech in other countries like Germany, Canada, France, Australia, UK.
When you make a globally available website, how do you "follow the law" when the laws of various countries are not compatible with each other? Do you geolock all tweets - Canada twitter is vastly different to US twitter? That doesn't sound scalable good!
Indeed; China doesn't like references to a certain children's cartoon / book character, and nearly two billion people do not take kindly to any kind of disrespect aimed at their prophet.
You can also look north to Canada where the American notion of “free speech” does not apply. There are reasonable limits on hate speech, obscenity, defamation and the like.