Simple: if you force me to make something I don't agree with then you are compelling me to support your lifestyle - and that infringes on my freedom of speech.

On faith? Majority of the world believes marriage is man+woman. If you force me to make a shirt, website, cake, etc? Thats making me create something that endorses that idea.

You can't claim to support freedom if you support forcing others to take part in stuff they disagree with.

Can you articulate how forcing someone to do something they think is morally wrong or evil isn't slavery?