Yes I am. Article II section I references the Presidental Oath of Office which includes his duty to "preserve, protect and defend the Constitution of the United States". His oath, in conjunction with the Supremacy Clause, require the President to not enforce laws he feels are unconstitutional. There is a large history and legal body of evidence, including several Supreme Court decisions, supporting this position.
The idea goes back to the founding of the country. While Washington never disregarded any laws Congress passed - remember there was no legislative history when he became President - his writings and the fact that he refused a number of Congressional requests strongly imply that he would have if he needed to.
Jefferson did refuse to enforce the terms of the Alien and Sedition Acts, which Adams passed, when he became President. He flatly stated that he deemed them unconstitutional and that he had a duty to not enforce them.
Ask yourself this question. If Congress, over a Presidental veto, enacted a law that shuttered every newspaper in the country - an obvious violation of the 1st amendment - would the President be required to enforce it until it was ruled unconstitutional?