Hi Jeffrey:
I have commented much about the slippery slope of deciding to award extra credit or not. I can argue both sides.
Personnaly, allowing some wiggle room (extra credit or extra consideration) on individual assignments makes sense because it's limited to just one category. But to add a whole category of just extra points really skews the grades, and is unfair to students who have truly earned their passing grades. So, in an indirect manner, extra credit is a fairness question, at least in part.
Regards, Barry