All you can say is the border is very porous and Mexico does nothing to prevent criminal activity, drug smuggling, and illegal entry by their population into the US. The situation adds greatly to the Mexican economy and is a drain on the US.
Who should pay ?
Obviously the Mexicans since they are the problem.
Its a bit like having a couple of savage dogs living next door that come onto your property because there's a hole in the fence. Yes you'd fix the fence, but you'd then get the cash off the neighbour - using small claims court if you had to.
