Well, now we're down to brass tacks, aren't we?
The idea of "valid reasons" is meaningless unless you have some basis for making a decision one way or the other.
The ability to make a decision implies some standard, which is either arbitrary, or it is not. And unless you've got something at bottom that says "this is always wrong," then all standards are arbitrary.
Let's address a single example to illustrate the point.
Probably the most obvious "valid reason" to condemn pedophilia is "because it could harm the child." Such concerns are meaningless, of course, unless you had some standard that says harming children is wrong.
If "no harm to children" is an arbitrary standard, then we can as easily reject the standard as the sex -- and the existence of people such as are mentioned in these articles shows that there are some who do indeed place the sex above "no harm."
And even if the standard of "no harm" is binding, there's still not necessarily a problem with pedophilia in general: adult-child sex might be allowable on a case-by-case basis, just so long as the child was not harmed; and then the debate is either over, or it has to procede on other grounds, with other "binding standards."
The very idea of a "binding standard" merely shifts the debate to whether or not any particular proposed standard is arbitrary.
Ultimately, this debate comes down to a single point: one must either accept that "it (whatever it may be) is wrong because it's wrong," or one has to conclude that all standards are arbitrary.
This takes us back to the question I asked before: is there any act which is intrinsically wrong?
Yes. When you seek to remove all judgements, you seek the lowest level of society. Seeking the lowest level of society, leads to a low level society which eventually leads to destruction.
Look at the corporate scandals, the destruction caused by Clinton, the moral depravity creeping into our society.
Any person using your idea will judge from what is good for himself with no regard to others. He also will lose the right to expect others to treat him fairly because they too will judge all from their wants.
How does he raise a family, care for a wife? What about his business ethics, his reputation in life, the sense of respect he has in himself and the respect from others? All these areas will be undercut by the total disregard for anything other than what he wants.
Sort of like a 3-year old trying to be a man, a father, a husband, a CEO, a policeman, a fireman.