As a society, we should consider if it is acceptable for a company to influence society via the way they moderate their content while being largely unaccountable to citizens.
That's not what's happening though. Society is holding them accountable, especially since Trump took office.
You just don't like that they fact checked and banned Trump. Imagine for a second it was someone like Hillary Clinton that got banned from Twitter for inciting a violent mob to storm the Capital to stop congress from certifying Trump as president. Would you be upset when Twitter banned her? Of course not. That's what makes your argument in bad faith. Step back and look at what you're really saying without Trump in the equation. It's ridiculous.
If anybody fact-checked Trump and found him wrong, why won't they simply let him present his evidence before Congress? Looks more to me like they found Trump right, and are trying to silence him because... because the truth would be their downfall if it ever came out into the open.