How could same-sex marriage laws be considered "anti-Christian"?Not really... and it also depends on what one defines as anti-Christian.
Certainly the redefining of marriage can be considered as anti-Christian. The current attempt to change the rules of Title-IX is anti-Christian and anti-parent. One could develop a list though you might not see it as such.
You're still free to practice as you see fit and celebrate marriage as you see fit. The only difference is that people who don't believe as you do are now similarly free.
Is your religion really opposed to the freedom of others?
Also: are you really opposed to the religious freedom of Christian denominations that celebrate same-sex marriage? From where I sit, the anti-Christian is you.
(Though I'm sure you'll tell us why you think those denominations "aren't Christian" or don't deserve freedom of religion)