I mean, if this guy has ever once done a cake for a bar mitzvah then there's no way he can possibly make a credible case that making the cake required him to commit blasphemy.
Do you assume evangelical Christians believe Jews are going against God by having bar mitzvahs?
Unless there's been some misreporting, then the baker going around and saying he serves anyone and everyone and he'd serve a same-sex couple an off-the-shelf wedding cake, is real scumbag territory. That's not what was reported to have happened at the time: the couple were kicked out as soon as their sexuality became clear. Probably on advisement from his legal team, but it's tantamount to lying now.
Why do supporters of the baker have such trouble with comparable scenarios. It's always a version of either (i) forcing a group that does not and has never served Product A, to serve someone Product A, or (ii) forcing minority group X to pipe out lettering "Kill the X's". Do people think that a same sex couple getting married is equivalent to a hate group preaching their worst ideas?
Finally, the common argument that the customer just needs to go somewhere else. Besides the awful feeling of being treated less than human, not everyone lives somewhere with abundant choices:
"A couple years ago, Georgia was considering a state law that would work to enshrine the redefinition of religious freedom discussed above. CNN visited a small Georgia town to interview florists there. Every one of the five florists would refuse to serve a gay couple."
Source: All you need to know to win an argument about the gay wedding cake case