To say that there is no right or wrong, is foolish, and it is simply a show of your own intelligence level. If you can't grasp the concept of what's a right moral desicion and what's a wrong one, you either have a dangerously low IQ, or you chose not to think about the outcome of your action. What makes something morally right or wrong is what effect it yields and in what context you action has taken place.

For example, you used stabbing someone to support your thought that although the person being stabbed would feel it was a "bad" the person who did the action could have believed it was for the greater "good." You may be right either way, but it depends on the situation and it's outcome.

If there is a terrorist about to blow up a plane with innocent people on it, and you stab him before he detonates the bomb and it saves all the people that was a morally appropriate action for the greater good.

However, if your on a plane and you stabbed the pilot and co-pilot in attempt to hijack the plane and crash it into the ground killing all the innocent on board, that is a "bad"

The reason, is the situation and the outcome.

In the first, your using a bad means to a good end, and the end doesn't always justify the means, but because of the details of the situation, anyone with half a brain can see it was a good. It was for the greater good of the innocent people, and whether an objective or subjective choice it yielded a good result on everyone around you. Although the terrorist will feel that you have done a bad thing, you have thwarted his attempt on doing an obvious evil act.

In the 2nd, your doing an evil act. You have a bad means to a bad end, and oncemore, anyone with a brain can easily interpret what you have done as an evil or a "bad."