democrats versus republicans in usa hatred,

why do democrats and republicans in usa hate each other so much, inuk we have three major parties, but we dont hate each other, if somebody says they vote conservative i dont start a hate filled tirade, its a free country, people can vote how ever they want, but in usa its different i regularly see hatred shown by both sides, screaming videos, when actually both usa parties are two sides to the same coin, in uk we have conservative and labour/socialist, and labour is going to win the next election for sure, so why?