Well....they are faggots.
Not to mention, God hates sin.
If they accuse somebody acting through faith in Christ as hating their behavior, they might be truthful, but now they will have to answer to the higher authority for their behavior.
Had the printer failed to warn them of their impropriety, regardless their local jurisdiction, then the printer would be held partially accountable for the sins of the homosexuals by divine standards.
IMHO, the printer acted responsibly and the homosexuals need to respect the freedom of religion of the printer. If they sue the printer, then they are attacking the printer’s Constitutional rights to exercise his freedom of religion.
Additionally, failing to avoid the printer, the homosexuals also become provokers of hateful response. Such provocation is the basis for many laws on vice.