"Laws gentle are seldom obeyed; too severe seldom executed." 1
Personally, as for convicted criminals, I take no objection to imprisonment; or, for that matter, corporal punishment, including putting the criminal, in certain circumstances, to death. What I do take serious objection to, is being a victim to criminals. Aside from taking all the personal steps I can, to lesson my risk of being a victim of a criminal -- I would like to live in a community which takes a full set of steps to discourage criminal activity. Punishment is one of these steps.
The plain fact of the matter is that people are driven to do, or not to do things by the twin engines of hope and fear. Punishment, I believe, is one of the pillars of justice; it is to be meted out mercifully but always to be measured to suit the crime. "The only true way to make the mass of mankind see the beauty of justice is by showing to them in pretty plain terms the consequences of injustice."2 With law comes the notion, according to Locke, of either reward or punishment.3 It should also be remembered that the primary reason for the law's existence is that it should be such that people need not feel the need to strike out against those who do wrong against them. It is entirely natural for individuals, when wronged by another or others, to seek revenge and retribution and that it is potentially harmful to the state, if the state, does not satisfy these urges; not much good will come of it when people take the law into their own hands; but they will do so, quick enough, if they see that the law does not give them, as the victoms, any satisfaction.
As for capital punishment: I take the moral high ground: life is precious. However, that life is precious, is no reason to object to capital punishment, -- indeed, this is the primary justification for capital punishment. A legitimate use of punishment is its use as a deterrent; so too, it is a legitimate use to satisfy the need which the victim and his family have for retribution (lex talionis4). Thus, in this question of capital punishment, both deterrence and retribution play a role; but, there is an additional reason: to permanently rid ourselves of murderers.