Paine most likely uses the phrase "l offer nothing more instead of 'l offer you many reasons" or "i offer a detailed argument," because
a. he did not want to seem like he was overwhelming his audience with a lot of unimportant details
b. he probably thought it sounded better at the time.
c. he implies that common sense will be easy to follow and he will only present what is necessary to make his argument
d. he knew the people reading the pamphlet were not very educated and needed everything very simple.