Iago and Evil

I found Iago's soliloquy to be a fairly profound look into the evils of his character. He uses many excuses such as suspicions that he slept with his wife, to justify his intent to kill Othello. Yet none of these excuses seem like plausible reasons to murder an apparently innocent character. One point of this soliloquy that I found to be very interesting is where Iago takes the positive attribute of the Moor having "a free and open nature, thinks men honest" and utilizes this positive attribute as an opening to hurt the Moor. Therefore because of these reasons, the reader is able to deduce that Iago is an evil character by nature, and he is not able to justify his plan to kill Othello with such weak and unsupported excuses.