You get silenced by karma when you have unpopular opinions.

You know, just how people used to tell homosexuals to not be gay when other people thought they were freaks because of it.

Individual comments effectively get silenced (or at least buried) by downvoting, changing the account you post with won't change that. You can get an account shadowbanned however which does reduce the visibility of all its comments but that's a different issue, I don't think you can trigger a shadowban automatically by downvotes alone (or maybe only in extreme cases).

What I’m saying is stop worrying about karma and talk your opinions. Karma is not money or air. Your opinion matters.

And what I'm saying is that you literally can't when you get enough negative karma. I have three HN accounts and two of them have negative karma and can't post without mod approval.

Or it just says: You're posting too fast. Please slow down. Thanks.

Then you must be doing something wrong. I, always, speak my mind. This sometimes backfires karma wise but on the long run i think it was minimal.

It's called having unpopular opinions.

That you're conventional enough to never stand out of the herd says more about you than anything else.