People have a right to discourage unneeded suffering and death. (I am not surprised to hear that a self-avowed libertarian doesn't know the difference between the DOI and the U.S. Constitution, since there is little to nothing about the Constitution in their moral-liberal philosophy.)
"People have a right to discourage unneeded suffering and death."
Write pamphlets. Preach on street corners. Try to convince people through discourse. Your right to discourage *unneeded suffering and death* ends when you try to stop someone from doing something that doesn't infringe your rights. That is what the rule of law and the Constitution is about; that is the ONLY way capitalism (the only moral economic policy) can work.
"since there is little to nothing about the Constitution in their moral-liberal philosophy"
You aren't arguing from the Constitution, you are arguing from your feelings and what you want others to do.