Please don't put him down. I always compare putting a horse down due to behavioural issues to putting a human down because of the way they act - you wouldn't.
If you have the time, funds, and the want, there is a strong possibility either you or a trainer could work him through this; trust is a big part of it. And like other people said, consistency is key, and there's a possibility he might be in pain somewhere. I don't have much advice for the actual kicking, since I've been lucky enough to never have that problem, but someone with experience with that could give you some tips!
If you don't have the funds, the time, or the want to put your horse into training, the best thing you can possibly do is find him a trustworthy home that you know will work with him and try to get him out of his bad habits. Sometimes a horse just isn't a good fit for someone, like some people don't get along with others.
I'm sorry I don't have advice for the actual kicking problem, but that's the best advice I can give you.