This is a common yet relatively unknown fallacy. The typical situation is this: Someone is defending some view or theory. That someone acknowledges the existence of a number of objections to the view/theory that he is defending. He then defeats these objections to his own satisfaction and concludes that there are no good objections. Presuming that the person is rational, this is where he ought to conclude that there are no good objections known to him. He should not conclude that there are none.
Interestingly, I found logician, Graham Priest, that commits this fallacy (oh well, even logicians commit fallacies but hopefully less or less frequently than other people). Graham Priest defends his dialetheism theory in his book In Contradiction. On pages 238-240 he defends a view about the transmission of obligations. He defends that view against some objections and then concludes:
“[…attempting to refute objections…] The principle of the transmission of obligation is, therefore, perfectly acceptable.” (p. 240)
Such a thing does not follow. It is possible and even probable that there are other good objections which render the view not perfectly acceptable.
or:
I cannot think of any good reasons why not-P.
Therefore: P
Jep.