The only explanation is that he decided that sending a message of support to his friends in the gay community was more important that applying coherent legal reasoning to interpret the law.
Admittedly, this is a serious accusation. Yet I think it can proven with a simple test: Ask Judge Walker if his reasoning applies to polygamous marriage. In the decision he handed down, Walker find no rational basis for denying this fundamental right to same-sex couples. But every one of his reasons applies equally to polygamy.
I am not claiming that his reasoning leads to an argument ad absurdum. That would be a lateral move from one absurdity to another. What I’m claiming is that, if he is consistent, Walker would have to conclude that his rational basis criteria effectively overturns not only the ban on same-sex marriage, but the ban on polygamy.