I would not make an argument even if I thought a client would accept it. If they are incompetent they will decide to use the GPL code with sloppy oversight, violate the terms of the GPL, then they will hold a little grudge against you for the advice that got them in trouble. Sloppy companies have no internal accountability, so it's your fault.

I use GPL code all the time at home and I would license many things GPL, but there's no reason to push GPL software at corporations. They should have limited options and spend money, possibly expanding MIT code, possibly just raising the price of engineers by keeping engineers occupied.