That is still sabotage and possibly extortion if they try to bribe the company. If they weren't providing a real good with the bandwidth they use I would imagine no court would find them not guilty of attacking the company they are targeting.
In a free for all spectrum, it is much harder to prove that a device is interfering with another, making prosecution lengthy and complex. In the current system, if a device emits outside of its regulated band, its certification or authorization is revoked and the device becomes illegal to sell and operate. The criteria to do so are clear and evaluable from an objective standpoint, unlike interference in a shared spectrum that may or may not be willful and debatable in court.
Besides, it's not as if spectrum being freely available will magically make anyone a wireless carrier; there is still a significant up front capital expense to erect cell phone towers, routing calls to the PSTN, handling billing and support. A further proof would be that a corporation could create their own wireless carrier over the unregulated 2.4GHz ISM band by installing Wi-Fi APs and delivering VoIP over that for much less than the cost of erecting cell phone towers over an entire city, yet nobody did that.
Sure, it somewhat works and if necessary, I can just go sit right next to the Wi-Fi router to watch some cat videos while warming some food. I'd rather have my cell phone always working, though.
Besides, if spectrum is unregulated, what prevents company X from interfering with routers from company Y, so that Y's products are perceived as flaky? I mean, even with regulated spectrum, there were still issues between LightSquared's planned broadband network and GPS[1], for example.
[1] http://www.gps.gov/spectrum/lightsquared/