How does antifa get away with it? Simple. They have friends and sympathisers in the media, big tech, justice department and government.

They can do anything they want and:

• the media will not report it or say they are peaceful protestors.
• big tech will let them organise on their websites.
• the courts will release them the same day, if at all they're arrested.
• the government will deny they even exist.

Soon they'll be deputised to hunt down Trump supporters.

Not quite true. Concealed carry laws, then permitless carry laws, then open carry laws, and also "stand your ground laws" have spread to most states.

Now, the OP is correct that non-government militias have been suppressed, but this started because of going after the freedmen in the South after Reconstruction ended, then socialist commie militias that were part of the 19th century labor movement. Today, when we need private militias, they don't exist in any meaningful form.

Note, people like Ben Franklin understood private militias. Prior to the revolution, he financed a private militia to defend against Indian attacks in his native Pennsylvania. The same problem existed then as today, the Brit gov thought it was close to treason, but cooler heads prevailed.

Notably, when people have tried to stop them elsewhere they were arrested and prosecuted to the fullest extent of the law while instigators (with criminal backgrounds no less) were released and even lauded. Clown world, man.

Yet the Supreme Court has ruled that LEO has no obligation to protect citizens.

Money. Jack Dorsey - the creator of Twitter is a huge donor of Antifa & BLM. Twitter also controls the hype behind every trend.

The purpose of militias is not to "stop that shit", it's to stop government doing shit like choking citizens to death. tl;dr - the rioters are doing the job of militias.