Yeah...Barry has very high morals and a lot of character/integrity. Still, there wouldn't have been anything immoral about him cleaning up the situation.
1) Barry didn't actually kill DeVoe, of course, so why should he have felt bad?
2) It wouldn't have been disrespectful to dispose of DeVoe's former body because DeVoe himself doesn't care about that body anymore.
What it comes down to is plot, as usual. And people are calling it "The Trial of The Flash" from the comic storyline, which is false. This is just "The Trial of Barry Allen".
I'm liking The Thinker as this season's villain. Evil speedsters were getting redundant.