I think a lot of people wouldn't really care if they didn't call it "marriage". To most of the country, and especially the conservatives, the term marriage is a vow before God. Christianity is the dominant form of religion in this country, and does not allow for homosexuality. I think that's where some of the problem comes from. Of course some people just want to push their beliefs onto others, conservatives and liberals alike.
Statements like that one just show the hypocrisy of people involved in organized religion.
"God loves everyone" "All your sins will be forgiven" "Love thy neighbor"
"Don't try to belittle my beliefs or flaunt your disbelief around me but make sure you answer your door when I come knocking and try to push my way into your house to force my beliefs on you"
"Oh but don't do anything we don't like and make sure you learn to believe everything we say as indisputable fact or you're going to hell for sure"
(insert huge eyerolling emoticon here)