The main point of note isn't so much the nastiness of the effect, as it is Wily being shown to have remorse for his actions, giving enough cures for everyone, where X-series Wily seemingly doesn't give a damn.
* Justify shrugs
That scene always felt out of character to me - remorse isn't like Wily, and neither is gratitude - so maybe it's just that the idea of the whole Roboenza episode being a test appeals to me..
Was that really the effect of the Roboenza? Because Roll didnīt turned into a serial killer because of the virus. The RMs of MM10 were just holders of the cure for the disease, they werenīt infected as far as I can tell.
It does say that they attack the city in the intro, so... Wouldn't be too far-fetched to say that the Lightbots get extra protection against such attacks, so it affects them less.
Dunno about the RMs, we don't get any dialogue or backstory so for all we know it could be Megaman being an intruder hurrdurring into their lairs that sets them off.