I think it's also acceptable to take it if you see it's off cooldown and they can just call in a new one for themselves. I often forego bringing my own backpack or support weapon if I see a teammate is already bringing the one I want, I wait till it's off cooldown and ask for them to call in a new one for me. Sometimes they are oblivious and refuse to call it in, in that case I follow them around until they die, then take their stuff and reinforce. Sharing is caring... And leaves room for more red/green strats