It really is a terrible rule. I don't recall any big discussions about it and certainly not any where the vast majority agreed to such changes.
If we had an XP rate of 2x or higher, leveling an alt for professions wouldn't be an issue. But at x1, without the ability to boost your alt, it takes far too much time...
I also want to point out that multiboxing in any form is prohibited on the PvP realm. Perhaps the devs didn't consider this, but many players use a level 1 alt only to reset the dungeon they are farming with their level 60 character. I suppose the devs wanted to prevent multiboxing in arenas and battlegrounds (which I fully support), but this rule is far too harsh. Please allow multiboxing, at least with the condition that one of the characters must remain at level 1.