So.
1. There were bad people on the site, whom other people (you included) wanted to shut up. The site refused to do so. This speaks to the quality of the site, no? They refused to censor something while there was a strong push to censor it - that means they will probably not censor you, when your opinion will differ from the opinion of powerful people. That means that a person should rather support the site that does not censor opinions the person does not agree with.
Unless the person hopes to always agree with the opinions of the powerful people even when the powerful opinions change.
2. The logic of the federal constitution prohibiting only Congress to pass censorship laws, as far as I get it was: if a business indulges in censorship, customers can drop it and go to its competition. That's exactly what I am doing - defending the American way of life one less purchase on Amazon at a time. Suggestion not to worry is rather strange in the context: the federal constitution puts the task of stopping censorship in private businesses on private citizens, me (and you) included.
3. Actually, I live in California and California constitution protects my right of speech from private censorship too! It even works - if a private business is a shopping mall, eg. But it does not work for Google or Facebook. Because people do not think it's important. That means a piece of paper, even if it is named "constitution" can't protect the rights declared in it - if people stop thinking these rights are important. Why shouldn't I be worried - I have a "living experience" in a country with the right of free speech in the constitution only.
A clarification. 4. There were extremists on the site making calls to violence. Actually, at the moment of the de-platforming it was about "Russian propaganda". Some factual information was labelled "foreign propaganda" and censored. Again, I have and enormous "living experience" in the country with a permanent ban on "foreign propaganda".
A puzzle. 5. that is neither censorship as a society would consider it nor is it problematic.
My English is not that good but a dictionary tells me that:
cen·sorship
/ˈsensərSHip/
noun
1.
the suppression or prohibition of any parts of books, films, news, etc. that are considered obscene, politically unacceptable, or a threat to security.
prob·lem·at·ic
/ˌpräbləˈmadik/
adjective
constituting or presenting a problem or difficulty.
To consider this neither a censorship nor problematic you should change dictionaries first (probably you all are tired of my mentioning my "living experience", but yes, I have that one too).