Nullius and DannyHamilton are spot on.

It's sad that people are getting bamboozled by malicious disinformation on this subject.

The _exact_ same thing protects segwit outputs from being stolen by malicious miners as any other coin: Following the rules is part of what _defines_ mining.  A miner that steals an output hasn't mined as far as nodes are concerned, their blocks will simply be ignored (and the peers relaying them eventually banned).

Segwit is no different from any other consensus rule in this respect-- other than some were introduced later than others, but many have been introduced over time.

We didn't see these same sorts of malicious FUD with P2SH though it was exactly the same-- I guess because back then felons hadn't figured out how to monetize that sort of confusion.