I think saying the accord has no repercussions is a strawman. Let's say it does: will the same people against it, suddenly support it? I think the answer is clearly hell no. You can read Trump's statement on the accord. It clearly talks about the climate target commitments being negative for America. That there are no repercussions is irrelevant. As one of the large nations, our agreement is enough to make it so America is obligated to perform (or at very least very close) or we lose credibility. Adding repercussions will only make it worse to the people opposed to the agreement. The reason to oppose is very clear, and Trump even said so: leaving allows America to continue polluting (concrete example mentioned: opening new coal mines). Leaving is the first steps in walking back on the progress we have made under Obama (coal was moving toward extinction, as it should).