What is being a jerk? He wouldn;t have to moon the guy while doing it. One would think that Roberts' views and philosophies would be well known to the other partners. I would see the jerky behavior in coming to Roberts for help on a case you would know that he found incompatible with his philosophy.
So either the other partner was a jerk or the other partner knew that the arguments presented in Romer did not conflict with Roberts' judicial philosophy.
You don't understand how law firms work. What you propose would be very bad form. When you're partners with someone, you don't refuse help you're in a position to give. Now, if this group had approached him to take the case and take lead, that would be an entirely different matter. I doubt his partners would mind at all if he would have taken a pass in that case.
Please keep in mind lawyers are advocates who don't necessarily believe the same way as their clients and often take cases they might not rule in favor of if they were on the bench deciding them.