Apologies if I've misread you. You seemed to be responding to the claim 'rationality training might have a negative effect' with 'the only solution is to try for ourselves'. I was saying the same principle could be applied to any number of things. If you were simply saying that whether something is good needs to be tested in practice, I agree. But I thought you were saying that we should try rationality training specifically, rather than other methods some think improve your life, (e.g. Scientology). If you're claiming that, then you need some reason to expect better results from rationality training than alternatives.