How so? Because the would-be theif isn't ripping off the government. He's ripping off his Jewish neighbors. They are the ones who will be required to pay more to make up for the slacker with his make-believe-shul. [Note: Stealing from a gentile is forbidden by Jewish law.]
Two men were arguing if it was mutar to pretend their house was a shul for the sake of avoiding taxes. First guy said "no way"; second guy said "Why not? Its only [gentiles] being defrauded."
So they went to [one of the great Rabbis of the previous generation] and asked him. He replied:
No. It isn't gezul akum. [stealing from a gentile] It's taaka gezul yisroel [stealing from a Jew.]
Unfortunately, this sort of theivery is now a way of life in too many Jewish neighborhoods.