Legal Theory? Run!!

We're currently discussing subjective and objective views regarding intent in criminal liability. Terribly interesting but it makes my brain hurt cause I can't decide which I like best. Take this case for instance.
Aside from the amusement that this case arouses in me, especially the: "You got me Dave, I'm dead." (if the man knows your name... shouldn't you think - "hmm.. maybe I should stop shooting"? - anyways, beside the point).
But anyways, the subjective view regarding this would say that since the man had no intent to kill the guy (he was just shooting at the gas tank - though I thought shooting at a gas tank was dangerous and would cause large explosions resulting in death (so he would have intent) but this didn't come up in our discussion of it so I must just watch too many action movies) he's probably just guilty of manslaughter.
But if you take the objective view, he's guilty of murder.
See, I prefer the subjective view. Where we just charge people with stuff regarding their intent. He did not intend to kill the man etc, but then I'm sorta like.. oh but now we're letting someone somewhat off the hook for killing someone.. see my dilemna? Sooo... sometimes the objective view (charging on whatever the outcome is) makes much more sense.
Another situation we discussed was about the man who thought he was transporting heroin across the border but it turned out it was only marijiuna. Should he be charged for transporting marijiuna or heroin? He may have only been transporting marijiuana (gotta love how many different ways I've spelt that.. its hard word to spell I tell ya, we didn't study that one in elementary school spelling) but he intended to transport heroin. So in a completely subjective view, you'd go for the heroin one, but objectively, the marijiuana.
What if it was the other way around? What if he thought he was transporting marijuana but it was actually heroin? Should he get the worse punishement even if he only intended the more minor crime?
You see why this hurts my brain? And really, can we just change it from case to case? Is that really fair? I don't think its fair, how are people to know what the law says if it changes from one situation to another?
My great amount of interest and enjoyment in all this stuff is making me pretty certain I want to take another Philosophy of Law class next year and the year after.. and maybe even find somewhere I can study it for grad school. But I can think about and research that after the semester is over - no time now. Anyways, meeting Diana for coffee or maybe icecream so I must be off. Hope I made sense in that above speil.