It's not a matter of whether it's theft. Of course it is.

But if you leave your valuables in the street unattended and then come back shocked to discover that they aren't where you left them, this is not a problem that requires new legislation to solve. The solution to preventing this from happening to you in the future is quite obvious and doesn't involve the government.

And if the government manages to catch the thieves, great. But if they don't, c'est la vie.