Student or Learner
Some argue that such research (human embryonic study) violates the sanctity of human life; others posit that the potential to alleviate human suffering constitutes an ethical mandate to proceed.
It means they are ethically authorised to carry on with the research.
- but more than just 'authorised'. If something authorised them it would be a license. A mandate is more of a command. The sentence is referring to people who think that because researchers can proceed they must.
I'd say it means an ethical obligation to continue on with the research since it could benefit many people.