You do realize that its almost 200 years after the war and there are barely any bottles left in the machines, not even speaking about the electronics which are needed to give cola bottle when cap is thrown in?
Any action or inaction in a position of power will always grant you enemies
Like said by Lexx, there'll be vending machines in the future. If they are needed to be fight over ( I find it stupid to place a machine as a reason to PvP) it debatable still. But they undoubtly find their way in.
If you want to make enemies, try to change something.
To me it only makes sense if they are in a place where it makes sense that they can get refilled.
This is an easteregg location. If at all, you use the dude in Boneyard Downtown (Fallout 1) who is a nuka cola addict as an argument.