I think you can compare meditation to the field of "medicine" or "diet." There are cranks and pseudoscience in there too, but I wouldn't write off the whole field as irrational. It's got a semantic problem too. If more people called it "mindfulness" or "focus practice" that would be more accurate for how most normal, secular people meditate. Maybe even calling it meditation vs. alternative meditation (like alternative medicine). LOTS of different forms of meditation, and not all I think are worthwhile. Some are better than others.
TM seems like a total scam/fake though, just like chiropractic, astrology, juice cleanses etc.