Infinite slag would be perceived as OP. In a team setting the potential to spread slag everywhere, with no downside could make the game a cake walk. Zer0 can spam his knives or loop deception kills, Maya is a godess of Elements, a well built Sal would be Behemoth with evety enemy slagged, Upshoot Gaige.. ect. I think it was a good move overall. Inf slag would be a problem for the challenge factor.
What is a man?! A miserable little pile of secrets!