I would admit to it being illogical, in that I didn't use logic to arrive at that statement. But it's an entirely rational statement: I arrived there via pattern matching, though, and not logic. Is it irrational when I look at a face and recognize it? If not, then why so with other patterns I recognize?

And it's not a conclusion at all; it's just an observation. People who are as obviously disgruntled as the employee in question often end up striking out. Some, a very few, strike out violently.

The employee in question has already shown evidence of "striking out," he just hasn't escalated past passive-aggressive behavior. I used an extreme example of striking out to throw it into perspective: He's not happy, and he's willing to do things out of spite, and that's a liability, even if he never ends up violent.

There are lots of scenarios that don't involve physical harm: Leaking confidential information. Cleverly hidden time-bombs in code that no one else understands. Lawsuits. Spreading discontent among employees.