I would say that by making a particular offence, the message you're sending is that this is consistent with a shared or collective sense of values—that this kind of property should be held in higher esteem. Certainly, Parliament can do that. I don't think it will have any effect at all in deterring those who would otherwise be inclined to disrespect that piece of property, but I think it might do something in terms of showing a collective sense of values.
But I think once you do that, you set up a competition amongst people who value certain monuments, and they will ask, “Why isn't our monument given the type of protection that this one is?” On the ones you point to in terms of religion and desecration of property, that's coupled by the desecration having to be motivated by bias or hate, so it's different from saying that it's not okay to urinate on the cenotaph but it's okay to go down the street further and urinate on the memorial for the firefighters....
How do you reconcile that this type of memorial deserves greater protection from Parliament than some of the others that commemorate values that are very important to some people? A lot of firefighters and others die in the service of their fellow citizens as well. It's hard to justify why this one should be singled out.