Not to be a stick in the mud, but morals are not someone's opinion. You do not decide your own morals. Morals come from the community. There are many things affecting what someone's morals will be but they are all external.
To go back to the thread topic at hand, the post-modernist in me wants to scream moral relativism which to a certain degree is true since one community will have different set of values due to having different influences. To go to roto's question at hand, it provides us with a problem because to say that their moral or ethics are based on "wrong reasons" is to make a judgement on what is right and wrong and superimpose such judgement onto some other system without considering their own differences and such. So to actually answer this question to any extent there would exist the need to elucidate what is meant by "wrong reasons". Are we referring to the immorality of masturbation based on old misunderstandings of human anatomy, as per the Bible, or referring to ones own moral or ethical basis?