But here's my problem: Fully aside from this guy being a genuine quack, why not just test his therapy fully and completely? Follow his specs and advice to the proverbial "T". Prove him wrong beyond a reasonable doubt and put an end to it.
I can see at least four reasons.
First, it's painfully unethical. Since these novel therapies are unlikely to work, encouraging patients to try them in lieu of real, evidence-based medicine is going to kill a lot of people. You cannot get institutional approval to do a trial unless you can demonstrate that your trial therapy is likely to perform as well or better than the existing gold-standard approach. Randomized trials these days don't divide patients into experimental therapy versus placebo; they're divided into experimental therapy versus current therapy.
Second, there isn't enough of anything to do trials of all the ridiculous therapies; we have enough trouble organizing trials of real, evidence-based therapies that are likely to work. The dollar cost would be exorbitant, but that's actually not the steepest cost or most irreplaceable resource. There are only so many clinicians available - doctors and nurses and radiation therapists and pharmacists - with training relevant to oncology, and they can only do so many hours of work in a day. Wasting their time on futile clinical trials means treating fewer patients with real therapies. Similarly, there are limited numbers of skilled laboratory workers, statisticians, and other scientists. Last, but by no means least, there's a limited number of patients with cancer. Recruiting large numbers of patients into useless trials means a shortage of patients for worthwhile trials.
Third, the quacks won't be satisfied anyway. One of the important parameters used in modern clinical trials is the establishment of 'futility' criteria. Essentially, they're intermediate checkpoints in the trial where it might be halted early if the therapy's results aren't looking promising. This is done in an effort to reduce wasting time and money on ineffective interventions; for serious illnesses the futility criteria help to limit the number of dead bodies. If one cuts off a futile trial of a quack therapy early in order to save lives, the quack is going to say that The Man shut down his trial.
Finally, if our response to quackery is to throw funding at it, we encourage more quackery. The persuasive charlatan will always be able to recruit more followers. If this iteration of the therapy is demonstrated useless in a full-blown clinical trial, after this round's money runs out he can just come up with a new variant on the theme, and demand fresh funding for another few years. Lather, rinse, repeat--we create an entire pathological, publicly-funded quack welfare program.