ok 3 things you need to remember before calling Malekith a douche.
1. hes an elf, and because of that you have to compare his doucheness to other elves doucheness.
2. hes the commander of an army, what commander of an army doesnt use tatics like he does unless they are oh so sad about losing any lives. hell, how many times while playing the tabletop do you sacrifice one squad so 3 others may get the jump on a particularly annoying group in your enemies army? its called tatics
3. the guy was, as stated before, told from his birth that he would be the next king, that combined with elven arrogence, makes him very very VERY arrogent, and probably very very pissed off when he was upsurped.