Can those who defend Trump's complaint here, and agree with the view that the United States is carrying too much of the burden of international defense, really be so naive? Do you think the Americans are defending against rival powers (Russia, China) out of the goodness of their hearts? 
They are keeping their most serious threats contained, thousands of miles from the continental U.S. itself. It is the logical strategy of a self-interested superpower. In this they are no worse than other empires in the past, or more recently the Soviets with their "buffer zone" of weak neighbouring states. Wouldn't an American defense of Canada be moved by the desire to keep the Russian bear away from the northern border? Pragmatism, not altruism -- what could anyone expect?