One bad transmitter in your neighborhood can cut you off from the hobby. Someone who's into linux and computers can follow an online tutorial to rig together an SDR. Look at a bunch of numbers or static, shrug and move on to a different project without disconnecting that anttena breaking an entire band for all of his neighbors. Then it's on those neighbors to go build a directional antenna and buy portable radio gear and then do their own "in the field investigation" to isolate which house is doing that, then go try to explain to the random person they are polluting a band and hope the person is friendly and cooperative.
In a perfect world the FCC would do that, but getting the FCC to act on small infractions like that is a slow and long process and often goes unanswered. Especially if you're not near a marina or a federal building or an airport. So one hackaday reader can take down ham operation in an entire area because they were just interested in a weekend DIY project.
People throw that "against the law" to limit the damage. But actually getting the FCC to prosecute these issues is a challenge in itself.