There is no "Correct" answer here so if you're looking for guidance, then you simply have to ask yourself what makes sense to you.
Don't be disillusioned by all the players responding here who wish to make this about "Integrity" or convince you that "No matter how you look at it it's cheating".
Throw all that bunk out the window.
They have their own way of seeing the world which may not be the same for everyone else. They're simply responding with what makes sense to them.
There is no Universal moral code that everyone must comply with. The fact that threads related to "self calling fouls" always incite a tremendous amount of activity is proof that there is a huge variation in the interpretation.
If there is any universal resource to rely upon for this game then it's the RULES. if the rules don't tell you what must be done, then obviously, it's upon your own discretion.
Incidentally....there is a reason that the rules do not require you to call a foul upon yourself. So use your own reasoning when addressing this question.
Everything we think, including all the moral issues are relative to the context of the situation.
Your opponent is responsible for participating in the game. If he's distracted, off buying a beer, going to the bathroom, talking with friends etc. and doesn't see the foul, why should you be penalized for his lack of participation.
On the other hand, if your moral compass has been programmed to believe that your opponent should always be informed regardless of the context....then follow that.
I can promise you, many of the responses on this thread who claim it's about integrity, would sell their grandmother under the right conditions.
Don't fall into the morality trap.....think for yourself.