All legislation is an expression of morality. Even building codes are there because of the prevailing moral viewpoint that a structure should serve the purpose for which it is designed, and that death from a structural collapse is a bad thing. Theft and burglary laws are based on the moral premise that stealing is wrong. In Islam, killing your daughter for dishonoring you is acceptable, an expression of Islamic morality. Someone's morality is going to be legislated. Your argument is pulled out when an individual wants to avoid discussion of the law being considered, and is a misdirection used to confuse the issue.
I was about to post something similar to The Fugitive’s comments. We already legislate morality.
But I will add...I don’t believe pornography is protected free speech.