That might be the case.  However, doing such a thing is not abnormal.  Were you against Rosa Parks for refusing to move to the back of the bus?  She started a movement with that act, which was also preplanned.  The same, in many ways, can be said about this.  This was one of the first cases that ever dealt with this issue, and has seen it go to many different courts to verify the decissions made. 

Regardless if they knew the baker would not sell them a cake or not, does not change the fact he was breaking the law by doing so.  There was no legally justifiable reason to deny making the gay couple's cake.