You are correct, but now you are getting into shades of grey more nuanced than

> Either you believe in an open internet or you don't. Either you're with us, or you're against us.

The distinction is between perfectly legal speech, and specific acts fraud or things that are direct, actionable, and credible threats to physical safety (e.g., bomb threats). This isn't a complicated blah blah, where we need a technocratic meta-god to put his thumb on the scales. The existing legal pre-computer legal frameworks cover these cases.

And if the literal nazis we’re actually using a private person to person (can be through a service) communication medium like a phone the number of people who want them deplatformed would drop to basically zero.

Your argument has to account for the fact that Twitter is more like public radio than a phone and that WhatsApp is more like a phone than radio.

To be fair I do see articles written pointing to the fact that hate groups are using signal or discord, the implication being that such companies are "platforming" those groups.

What happens if the literally nazis robo called thousands of people with nazi propaganda?

They might get cut off for robocalling, but (if the telephone company is obeying the law) in a content-neutral way.