Just like any good judge knows, there are many factors that go into the seriousness of a sin. Intent is a big part of it.
If I shoot someone, is it murder in the eyes of the law? It depends. Was it my neighbor who I can't stand, or was it a burglar who was walking towards my daughter's bedroom?
Did I make the xerox because I hate my boss and I'm secretly happy to stick it to him with my little acts of rebellion and theft? Or did I make the xerox because it was necessary and is an accepted practice at my office?
Making a 5¢ xerox could easily be a mortal sin. Or it could be nothing. It depends on more than the act itself. God gives us a conscience for this reason, and He gives us the Church to help us develop it.
Yes, in judging the seriousness of a sin, I certainly agree that you always have to take into account the many factors which caused you to have gone wrong. But I am thinking here that, after taking into consideration all of those aforementioned factors, there are some sins which you commit and they do not prevent you from presenting yourself for Holy Communion, while other sins would prevent you from presenting yourself. For another example, take the case of a "white" lie. It is a sin to tell a lie, is it not? But some lies are not all that bad. For example, if you want to get rid of an annoying sales person who has called you in the middle of dinner and when you answer the phone he tells you that he has the best duct cleaning service and he asks for the lady of the house. He goes into detail about the cleaning process, and the fact that he also does carpets, etc. You then falsely tell him that you are sorry but the lady of the house is not here, she is out of town and won't be back soon and you hang up. This is so you can join her and the rest of your family for the delicious meal which your wife has prepared. My guess is that such a "white" lie told for the sole purpose of getting rid of the annoying telemarketeer and joining your wife and kids at mealtime would not prevent you from presenting yourself for Holy Communion, even though it was a lie? Actually there are two lies here, the other one is when you told him that you were sorry. You really weren't sorry, but you were annoyed, and it was your wife and kids who were sorry that you had left them at dinnertime for this annoying sales call. You were just being politically correct and wanted to get rid of him ASAP without hurting his feelings.
To sum up, for a Roman there are two categories of sins:
Category I: This sin, after all due reflection and consideration, would not prevent you from presenting yourself at Holy Communion. Of course, you still must have the proper intention and attitude to do good and to avoid all sin as best as you can. The Roman says that this is a venial sin.
Category II: This sin, considering the gravity, the intent and the motivation, is serious and does require you to confess it before receiving Holy Communion. The Roman says that this is a mortal sin.
This is one area where I suspect that some Romans would have difficulty in adjusting to - if there were no distinction made between the two cases.