From slavery, racial segregation, gender discrimination through same sex marriage the US seems to be pretty slow on adopting legislation towards equality. What legislation are you thinking about?
You think the United States was worse than Europe in terms of racial segregation? Europe ended slavery not long before the US, and Belgium and Brazil continued to uphold slavery for decades after. The only reason that segregation was more of an issue in the US than in Europe is because of the general lack of racial minorities.
Before the 1960s, Europe treated the people of color in its colonies with just as much cruelty as America showed to its minorities.
Also, I think that gay Americans are nearly as able to get married as the gay people of Europe. Approximately 116,000,000 people live in states where gay marriage is legal. Therefore, about 37% of Americans have the right to marry a member of the same sex.
Given that gay marriage is not allowed in Italy, Ireland, Scotland, and the entirety of Central and Eastern Europe, I'm not sure if the US is any more homophobic.