Segulahs

I was talking to a friend last night about segulahs. In general, I think they are extremely detrimental and completely defeat the purpose in which people comply with them. I think the problem with them is that a person relies on completing a ritual rather than relying on Hashem. And when the completion of the segulah fails to bring about the desired result, the blame is placed on Hashem, rather than the individual. I have no problem with a person reciting Tehillim - I think it draws one closer to G-d, however, using it as a bargaining chip to get what you want seems counter-productive. I think in general, people would be much better off actually doing something to achieve their goal rather than some unrelated ritual that supposedly will bring about the desired event. I don't really understand the reliance on segulahs, and from what I understand, feel that they should be completely antithetical to a Torah life. So why are they so prevalent?