It's insane and horribly disrespectful. I don't understand the animus either. I just sent a $ donation to the maintainer.
The response to this bug is completely over the top. He found a security issue in an optional feature, immediately fixed it over the New Year holiday, and provided clear documentation about who was affected and how to address it. That's exactly how responsible disclosure should work.
The level of hostility - especially over adding optional features that people can simply choose not to use - suggests this is more about bandwagoning than legitimate criticism. We should be supporting developers who maintain critical open source infrastructure, not attacking them over a prompt response to a contained issue.
ZFS is maturing on Linux and the codebase and general focus is on Linux today.
Hardware compatibility and mindshare are also big factors.
It seems like a subset of the TrueNAS community reveled in the fact that Core was FreeBSD-based. Maybe just a bit contrarian.
I've had meh experiences supporting, repairing and transitioning installations away from ixSystems. I wouldn't advocate their offerings in the first place, but it does seem like you have unrealistic expectations from ixSystems.