That's part of it, the trust model with drivechains is basically that 51% of miners can steal coins from the drivechains. But this is an opt-in risk so I don't mind it so much (doesn't affect non-drivechain users)

The other part, that I worry more about, is that drivechains can end up becoming shitty block size increases. The problem is if the drivechain is important and successful, the miner may end up incentivized to monitor the drivechain, which gives big miners with more resources a financial advantage, this contributes (an undefined amount) to mining centralization, which is the enemy of bitcoin's continued survival.

Is it a big enough problem that we should block all proposals that enable it? I dunno, but I'm not willing to bet bitcoin's future that we know the answer, any time soon.

Whereas there are several very safe and well understood upgrades (like CTV) that don't introduce risks like this.