There's an article that outlines some specific costs <here>.
Seems to me (and the article acknowledges it) that this is less a problem with capital punishment and more a problem with how bureaucratic it is.
damn i must be the only one here who hasn't tried marijuana...
I've never tried the stuff in my life.
Let me explain the difference between the so called "slippery slope" of marijuana and what you said... marijuana is already illegal (well at least in the US). Also notice that I didn't exactly define what the next high is... people who try marijuana typically also experiment with other drugs especially youths... which can either turn out well or turn out badly due to the situation.
I'm not saying that everything corrupting people to do more illegal activites is marijuana... but in various cases it does play a part.
And again, thanks to religious extremism, things like 9/11 happen. According to your logic, that means we should ban religion, just in case.