Well I can see the idea of a gay couple raising a child sounding like a strange and dangerous idea to someone who hasn't been exposed to it, religious or not. For example: couldn't this lead to children being confused about their own sexual identity?
But one of the reasons for this ruling was that it was shown in the court-room that children do as well when raised by a same-sex couple as by a heterosexual one. It then follows that recognizing those couples would be even better for those families.
We live in a hetero-normative society. Hetero couples are everywhere in media and popular culture. I'm pretty sure that kids being raised by same-sex parents can see that different people have different sexual orientations and work that out.
I'm sure it's harder for young gay people to have straight parents than for young straight people to have gay parents, yet nobody ever worries about that scenario.
But one of the reasons for this ruling was that it was shown in the court-room that children do as well when raised by a same-sex couple as by a heterosexual one. It then follows that recognizing those couples would be even better for those families.