The result of an improperly implemented url is being penalized as playing black-hat because of duplicate content.
That’s not entirely accurate. If it were, many many many sites would not be in Google’s index.
And I don’t think there’s anything wrong with redirecting from non-www to www, or the other way around. It’s simply a case of personal preference. I have yet to come across hard evidence that one or the other, or not having a canonical URL, is a terrible thing. It is best practice, but it won’t kill your site if you’re ignorant towards the whole thing.
All the best with your site!