Sometimes Violence is the Answer?

I am a firm believer that sometimes violence is the answer, for example Just War or protecting the weak.  Sometimes, during scripture reading I come across the subject of violence.  Many think that all violence is wrong, and shape their doctrine and scripture interpretations to match.  Years ago, the older folks would often quote the phrase vengeance is mine saith the LORD.  However, many versions of the Bible say that thou shalt not murder, not kill.  There is a time to kill and even Jesus said that there would be a time when you would have to take a sword.  Today, as I was chanting the assigned Psalms for today, I ran across something about the LORD hating those who take pleasure in violence.  Again, this can be taken two ways.  There are those who would be happy to cause suffering of others or gain by it, and there are those who would know that it is sometimes necessary and do neither.