> So because some idiot somewhere wrote a 100 assertion unit test we should ban anyone from writing even 2 assertions in one test?

You're falling prey to slippery slope fallacy, which at best is specious reasoning.

The rationale is easy to understand. Running 100 assertions in a single test renders tests unusable. Running 10 assertions suffers from the same problem. Test sets are user-friendly if they dump a single specific error message for a single specific failed assertion, thus allowing developers to quickly pinpoint root causes by simply glancing through the test logs.

Arguing whether two or three or five assertions should be banned misses the whole point and completely ignores the root cause that led to this guideline.