Paine's purpose is to prove the king is no better than these types of bad men.
Paine is saying the king is no better than murderers and robbers and is just as likely to get help from God as they are. (Paine is saying if God is not likely to help a murderer, then God won't likely help the king, either.) The king himself is a murderer and robber, thanks to the way England engaged in war and taxation. Paine's point is that the king is just as immoral as a murderer.