The United States has bad relations with Russia because of their human rights, but boycotting the Olympic games will not solve this problem. When Carter boycotted the games in Russia, it did not end the Cold War, but it did make him extremely unpopular. Boycotting the Games would not solve anything.
The Olympics represent a lot more countries than just the country that is hosting it. The United States should be there to support the countries that it does believe in. It should also be there to support its own athletes. They have worked very hard to get where they are and for many of them this may be their only shot at the Olympics.