Your last sentence is dishonest. Casings fail all the time and this is how the water table can become polluted. It's not a small risk at all. All it takes are fly by night crews doing sloppy work and many of them are. No one's regulating them so they do what the fuck they want. It all comes down to the bottom line--making money.

I live in the part of Texas where fracking was developed and have been around it for years. Our county has been plagued with saltwater waste being randomly dumped in rural areas. Our sheriff has to patrol to try and catch waste water haulers dumping fouled water. I personally have listened to supervisors in charge of well production brag about the methods they use for discharging methane so they get around EPA monitoring and requirements.

I don't think fracking should be illegal, but it is certainly very poorly regulated and Americans will come to rue the day as aquifers and ground water give way to infiltration from poorly implement casements and improperly capped wells.