In can think of a great many things Americans should be ashamed of in regards to the government letting the head of state of an ally address Congress is not one of them.
Naturally, you've missed the point. It wasn't that he addressed Congress. Many have before. It was that he was invited by the Speaker of the House instead of the President (and at a time when the person in question was running for office in his own country), and it was done specifically to wrestle control of foreign policy from a sitting President, and secondarily to help a foreign leader win an election. That is not only a case of a foreigner interfering with the governance of this country, but a case of a political party using their position in Congress to interfere with a national election in a foreign land.