Obviously the concern is an escalation of that war which pulls NATO into the conflict fully. I don't believe that's a likely scenario, but being deliberately obtuse isn't the right way address that somebody expressing that concern.
The argument that was made (and that was not central to the post at all, despite everyone jumping on it) is the slow erosion of freedoms that may lead to less restraint also in foreign affairs.
UK politicians have been periodically demanding NATO engagement, though this one is from 2022:
