There doesn't need to be any excuses ...
... unless you can show us where in the TOS it says that tanks have to pull at least two packs at a time?
Actually says that, not any lame "this general statement means this specific thing for no better reason than I want it to" nonsense. Being cautious is not griefing. Hell, going AFK to answer the door or take a poop isn't griefing, it's just part of life when you queue with random strangers.
And as other have stated, if you want to dictate how the tank behaves in a DF party, queue as a tank.
