You don't prevent trolls and shills, you block them - whitelist style. Communicate with people who have established a good reputation with you, or one or two or three degrees removed from you. Spend time with anonymous when you feel like it, maybe turn some of those identities into trusted friends, but always communicate with some kind of secure ID- even if that ID only lasts for a 10 minute back and forth exchange.

A major not completely solved problem with cryptographically secure anything is: key management. Ultimately you might carry some kind of switchable RFID key with you, switched off until you're ready to authenticate for some reason.

one person can open multiple accounts in multiple networks.

No problem with that, unless you're expecting to count heads accurately. If one person is creating the content of ten using ten accounts, is that a problem?

Facebook forces people to have phone numbers and there’s still so many bots and shills there.

I don't remember giving FB my phone number... with burner phones that seems to be an intentionally lame approach.

I think there’s so many ways for bots to happen that it’s like playing wack a mole.

I don't think you ever stop them, you just ignore them like junk mail in your physical mail box, except with secure IDs you can automatically filter them without even a glance.