If you want a proper analogy, try the Mediterranean. In fact, NATO countries are a significantly greater part of the coastline there, than Russia on the Black Sea. Or say the North Sea, or the Baltic. In fact, NATO has much more of the Black Sea coastline than Russia. (Turkey, Romania, Bulgaria) So, in fact, we should presumably be outraged than Russian naval ships are on the Black Sea. You were asking how we would react to a situation like that - well, you've got your answer.