it's easier to appear better if you have a defensive identity because you can just hang back and always do the safe play. Usually those Dmen have the size to back that up as well, although I would say that teams that rely on these types don't succeed unless they can get more Dmen who will push the play forward.
Offensive Dmen are expected to play in all three zones, not just the defensive one. As a result they get caught up ice a lot more and their mistakes are magnified because the mistakes are often dramatic. They often get labelled as having a lack of hockey IQ, when it really amounts to them just learning the NHL in the style they play, and that it takes time. As they develop their hockey intelligence grows, so much so that I would say that a developed offensive defenseman knows the game a lot better than a defensive defenseman (usually)
To answer the question, yes, there is a stigma against offensive defensemen and it is not all fair. Even those safer defensive types need time to grow as well, and until they do they often spend time in the defensive quite a lot, and look extremely clunky when they are tasked with pushing for offensive more.