(WARNING: This is kind of a dark philosophical position.)
Is self acceptance a matter of convincing yourself that there is nothing wrong your behavior?
I've known all my life that there is something wrong with wearing and using diapers based on desire rather than actual need. Some people will justify this behavior on the grounds that it isn't harming anyone, but in reality, this behavior does expose yourself and others to potential harm. Much like drinking and driving in itself isn't harmful but is still wrong because it increases the potential of causing serious harm. The fallout from ABDL activity isn't lethal, as it is with drinking and driving, but it still is capable of causing serious emotional harm. It ruins marriages, the basic building block of society.
There are many ways to rationalize this behavior: it's not my fault; I didn't ask for this; I'm not responsible for how others think; it's harmless; everybody has something to hide; other people do things just as bad or worse; I can live my own life any way I choose. But it's not always easy to separate rationalizations from delusions when it comes to moral values.
The bottom line for me is, self acceptance means accepting myself as I am right now - a creature with ambiguous moral values that may never change.