You have to think on a different plane of existence to be able to say yes to that. But all the giants out there did... Hawkins, Newton, the Wright brothers, Einstein. They all embraced three words that form a great truth.
Wrong is subjective.
Why put words in other people's mouths? Einstein's relativity relates to frames of reference. Newton was a hardcore Christian, and would never have said that morality is relative. Defend your own opinion using your own logic. No need to appeal to authority.
It's a code generally instilled from parents from a set morality and it's up to that individual to accept or deny specifics in that code. "Personal feeling" don't really enter the equation. Morality exists to keep the social structure intact. Sounds like it's rational to me, no matter what constructs are used. A lot of the moral code from Christianity is a remnant of living conditions when the moral code of the Hebrews. Those descending from that code have kept a lot of that overseeing code in place and has become more of a traditional thing. George Carlin in his famous 10 commandments bit deconstructed this code quite well.
This is all good. But if something is "rational" then it isn't subjective or culturally bound. The laws of motion are the laws of motion. A culture that creates its own laws of motion will never get rockets into space, regardless of how many objections they have to Newtonian mechanics (unless they create a more explanatory theory, aka Einstein). Similarly, if morals are objective, then it isn't up to the individual to accept or reject them according to his or her whims. If our objective is the well-being of all people (or whatever), then a moral standard either advances that goal or it doesn't. Cultural sentiment notwithstanding.