We are all incapable of coming to a consensus about what is acceptable. This is pretty much the same as saying there are always disagreements in politics.
Whatever you permit to be used against your opponents is certain to be used against your friends as well.
I agree, you'd need a way to verify every machine is running the the open source software. The risk are too great you'll fail and the rewards for anyone that can hack the machines too great.
To say a machine hasn't been hacked is trying to prove a negative.