I agree with you 100%.
Which begs the question - why do people vociferously support pornography? They must either want it easily available for themselves, or applaud the destruction of morality for some other reason. For instance, those who support socialist revolution greatly value the destruction of social order, since it helps their cause.
A third reason might be that if a person is attached to some form of vice, a culture that tolerates or promotes any and all vices is more comfortable.
Depends what you mean by "vociferously support." I vociferously support the regulated legality of pornography, although I don't consider myself a supporter of pornography, not because I want it or because I applaud the destruction of morality, but because using force to combat non-rights-violating vices is wrong.