The bakers did not discriminate against anyone.
They serve gay folk all the time and served this person.

No-one, whatever their trade, can be made by law to write stuff that they disagree with.

If you can be awarded £500 for every refusal, why wouldn't people demand lefty businesses produce right wing material?

Muslim businesses would be a really easy target.
"Support Gay Marriage" would catch most of them.
"Support Free Expression" with a cartoon of the Prophet would get the rest.
Would you be happy with those consequences Steve?
Not just a "what if" but a "why not"