Would legalizing gay and lesbian marriage under the notion that equality is for all open a can of worms?

I’m pro gay and lesbian. I feel they deserve the right to marry. Couldn’t one argue however, since the gay and lesbian community is claiming equality for all and the right to marry anyone for all, it would leave incest open for marriage licenses as well? For instance, say a father wants to marry his daughter, and they claim they are in love, and they stand behind the “equality for all”? I wonder what a gay or lesbian person might think about this.