These are unmoderated, just spam filtered. Forums, social sites and video sharing sites are typically not one of these, and the distinction is important. The most important distinct piece is ownership. Shen you signed the Terms of Service with say YouTube, you granted them rights that vastly exceed ones a common carrier has.
It is analogous to creating your own postal service or phone company that only lets you send letters to users of the same postal service or phone company. The service is only useful due to network effects.
I've had SMTP servers which have extremely high deliverability rates hosted for <$100/mo for over a decade.
The capital expenditures are nowhere near comparable. The regulatory burdens are nowhere near comparable.
Email providers are not common carriers. Its very easy to just sign up for a different email provider. Its easy to buy a domain name and update MX records across literally hundreds of commercial providers eager to have your business. And even if every single host bans you (you really should then question what you're doing if nobody wants your business) its still technically possible to go it on your own. And once again, as long as you're not being generally abusive its possible to have good success.
Comparing getting banned from Gmail might as well be the same as comparing getting banned from McDonalds. McDonalds isn't a common carrier no matter how much you like Big Macs. There's plenty of other restaurants available.
You are omitting telephone service, which is also a common carrier despite being arguably more competitive than the Big 3 cloud providers.
That's where I personally would come down. This decision is ridiculous; social media companies are highly competitive. But I am much, much less comfortable with AWS kicking off Parler.
Because it's hard to impossible to get alternate services for roads, water and electricity, i.e common carriers. But there are plenty of neo nazi forums, Gab, Truth Social, Parler, 4chan for racists to express and spread their views.