I seem to agree with ShoeGaze alot
Klown does have a point too. Many people complain about sniper precisely for the reason that they want to be able to run amok without getting shot. They don't have the skill or brain power to be able to cope with snipers.
Put 12 allied snipers vs 4 competent germans and who will win? It's not that snipers are too powerful. It's the lamebrains who can't figure out how to deal with them.
You cannot assure balanced, even teams. For one thing, I have seen 20 Allies vs 10 Germans in a game or two. You would have to enforce even team numbers. But even that won't work since skill varies. So maybe balancing out the number of kills per minute would be the best way to even the teams. This would make players switch teams automatically as required.
Even with limited snipers, you can end up with a bunch of dummies on your team with SMGs. How often do you see a team mate try to use a Thompson like a Garand? They take aim at a sniper from a long distance, and then squeeze and hold that trigger for dear life. Of course, this just announces their location and results in their death. Then next game, same thing.
To make it fair and fun, you would have to control the types and numbers of weapons, and the types and numbers of players on each team for each map. Obviously this will never happen.
I do think it would make sense to let the admin limit the weapon ratios. But picture this: some dummy gets the 1 sniper rifle your team is allowed and won't give it up. Have fun!