I briefly touched upon the limitations and fallacies of the LoA as a magical wish-fulfilling method in my post in the Karmic Debt thread
Basically, putting into motion a certain thought or desire isn't always
going to work in your life even if you put in strong, sincere emotion, and do it faithfully, without entertaining thoughts of failure; the reason is that if you have stockpiled a mountain of Karma counterproductive to that desire in this life and probably in numerous previous lives as well, and the time has come for it to bear fruit, then riches etc will not remain in your life. You will attract money only to watch it slip through your fingers. That's an extreme case, of course, but the Law of Karma is basically the Law of Attraction at work that your conscious mind doesn't perceive.
This is not to say that we should not make any effort towards greater happiness, or whatever your pure desires in life may be; all it means is that everyone will never become a Steve Pavlina or Joe Vitale or Bill Gates - those guys already had the samskaras
(latent pre-programmed mental tendencies) to attract what they fairly easily did into their lives. Hard work and intent manifestation was only a small part of the equation, the tip of the proverbial iceberg.
As regards people "creating" their cancers etc, I would not be so simplistic and say that their thoughts alone attracted the disease, but it is
true that "you" create "your" own destiny. It is never a genetic "accident" because "God" likes to play dice and you lost out in the cosmic lottery. As we sow, so do we reap. What goes around comes around. We always create our own suffering, whether consciously or unconsciously. So yes, we did
attract those illnesses into our present lives. Our thoughts and habits in this life may have been perfect, but that doesn't mean we didn't come into this life with engrams in our subtle bodies already ready to be expressed.
Here's the kicker though: we are all one collective consciousness, the same source manifested as different bodies, like holographic images of an underlying formless reality. So, in essence, by wishing health, happiness for ourselves, and functioning from a pure loving consciousness, we wish it for the entire universe. Hence, "love thy neighbor as thyself"; because loving him/her is loving yourself also, and in turn loving the universe.
Of course, all what I have postulated presupposes the theory of reincarnation