This country was founded on the ideal that freedom of speech should be protected and preserved as a fundamental right of each individual. It is not restricted to speech as approved by some government censorship board or decreed acceptable by a scientific consensus. It is not restricted to speech that does not offend religious authorities or contravene politically correct dogma. Freedom of speech encompasses speech that is incorrect and short-sighted, speech that offends me and you. The many reasons you cite for restricting speech are many reasons that justify a repressive totalitarian society.
As for YouTube’s supposed right to restrict speech, it should be very limited. We have to recognize that large social media network such as YouTube has attributes of a natural monopoly that potentially gives it power to abuse its position. It provides a communications service, but that does not give it the right to tell us what we can communicate. The electric power supplier does not have the right to force us to use appliances it provides. The phone company does not have the right to censor our phone calls and tell us what conversations are allowable according to its community guidelines. Our internet access provider does not have the right to tell us what we can put on the internet. In every other area where we communicate with one another the American paradigm favors free communication over censorship. Our system was founded to protect the rights of individuals against the abuse of power by government authorities. We also have a long history of law and custom preventing private concerns from abusing their market dominance to usurp our rights. Your employer can’t tell you what to say or how to say it or what to buy or when to buy it. Grocery stores can’t band together to tell you what religion you must follow. The transit workers can’t insist you wear a political button favoring a fare increase.
There are a few exceptions to allowing unlimited free speech. One might be a restriction on plotting violent crimes. Another might prevent sex slave markets or drug sales on line. Still another might be a prohibition against broadcasting security secrets such as nuclear launch codes.
None of the exceptions prevent the free debate of political views. The cure to bad speech is more speech. Eventually the bad ideas get defeated by good ideas. Free speech provides no protection against libel suits for spreading malicious falsehoods against others.
The act of censorship by YouTube was a watershed moment where a private concern tried to dictate what facts and opinions we are allowed to hear. You may be happy now if they suppress ideas you don’t like, but as soon as I am in power, I’ll force them to suppress every idea you favor. Or maybe we could both agree this instrumentality of thought control is a horrible threat to human dignity and endeavor together to keep it from ever strangling free speech again.