Kosher laws and do we need them in today's world? ?

Why is it that religious Jews use one set of dishes and utensils for meat, and a different set for dairy? Most of Mosaic laws governing food consumption make sense, but the plates and utensil ruling gives me great cause to wonder. And before I forget, why can't a gl of milk wash down a hamburger? Better yet, why is topping a hamburger with cheese also a no no? Will some nice Jewish person out there help me out on this? Like meaningfully. Please? Mike