Whilst I don't disagree with people finding his comments offensive (they simply are offensive), I would never go to lengths of denying someone his freedoms (and that's what any arrest would lead to) for being an idiot.
I think the only people that can really complain about his comments are those that would be directly affected by it, e.g. servicemen who are friend's with that guy on Facebook. And they SHOULD be able to file a civil complain about him. If he's a repeated offender, make it a criminal offence and take it one step further. But be reasonable while doing so, people walk free for physical racial assaults and that doesn't seem to bother anyone here.
Nobody should be allowed to "call for justice" because your neighbour told you that he went to his mate's house last night and his mate made offensive comments about army men.
This is what it comes down to. Also, see my edit to my previous post.