Be careful when paraphrasing and applying intent. Here's the part your actually refering to, for the record:
The rules for resolving attacks have been written assuming you will make the one at a time.
However, it is possible to speed up your battles by rolling the dice for similar attacks together.
So, if I fast roll the plasma weapons in my squad which rule, exactly, have I broken? Is it the part where I'm speeding up my battles by rolling similar attacks together? Or the part that isn't an actual rule, but a clarification of the "normal" rules?
Also, before you answer, do me a solid and take a step back from the computer and get a breather. That whole post reeked of saltiness (4 instances of "unfortunately" in response to my one? Really?) and, honestly, if you're gonna get upset over people having a different opinion than yourself (one they can back up via the rules, no less), then maybe
YMDC isn't the best place for ya.