Spam is censored, the vast majority can't even be sent because of SPF etc
You can pick a different server if you don't like the censorship on the one you're on, that's the whole point
To the spammers it's all great content you should be getting. No one's deleting your messages on your own Mastodon server, they're just not copying it to their server, what's the problem?
1. Spam is filtered, not censored. I can still see spam in my "Spam" folder if I want to. Mastodon doesn't merely filter "bad" content; it prevents you from seeing it even if you want to. It would be the equivalent of email actively deleting spam, and "spam" includes an email that suggests vaccines have side effects.
2. It's easy to see that it's not for the benefit of users. They could easily mark things as toxic (perhaps by category, or by who marked it as toxic), and let users filter out what they want. It's not about helping users. It's about controlling users.
3. "Spam" does not include contrary political viewpoints. There's a difference between a viagra ad. I don't want my uncle sending me political rants, but I certainly don't want google deciding I can't read them.