Failing a drug test pisses me off way more. I can see how someone can miss weight one time if an injury prevents them from training. Although it is insanely disrespectful to your opponent who had to cut weight and now fight a bigger fighter who didn't have to work as hard to cut down, I see how some of these guys rationalize it in their heads. They think because they drained their body trying to cut the weight, or cause they had some small injury that prevented a 'perfect camp', that missing weight isn't that big of deal. But it is a big deal, and should be dealt with accordingly.
If you roid you should surrender 100% of your purse to the opposing fighter. If you miss weight you should surrender 50%.