I take your points, however the first thing to remember is that Strategic weapons are a political rather than military tool.
It is therefore the politicians who decide whether we should have them and whether we should use them. It is also right that they should also be the ones to pay for them out of central funds and not to divert money from other "military" projects.
The second point is, do we want "Nuclear Weapons" or do we want a "Nuclear Deterrent". We currently have a deterrent, the distinguishing factor being this CASD that you point out. This makes me feel secure. I know that whilst we have this, no country would do, or allow to be done from its soil, a major attack on the UK that would change our way of life. Specifically because of the damage that could be done in retaliation. The fact that we would almost certainly do nothing is irrelevant. the important thing is what we might do, and there is no realistic way of stopping what we might do.
All of these things disappear when the CASD is stopped. There is a huge incentive for state and non-state actors alike to strike first. Similarly, the policy of "strategic ambiguity" that we have pursued would be destroyed. Should there be an incident, the media would swarm around Faslane to see if a Trident (or successor) boat would sail. Imagine the reaction if it did. It would certainly not help a peaceful resolution to the incident and politically who would have the bottle to make such a public show of force? They would genuinely be white elephants then.
It is therefore CASD or nothing.
The third thing is, the threats we face. Currently we are faced with a large terrorist threat, for which Nuclear weapons are essentially useless. In the future it is thought that we will face a large threat from cyber terrorism/attack. Again, nuclear weapons are largely useless in this respect, other than as a last resort (think EMP). However, there is clearly a threat from such states as Iran and North Korea developing nuclear weapons. There is no reason to doubt that they will eventually perfect these systems and also, there is no reason to suspect that in response or otherwise other states will not follow suit. It would therefore be irresponsible to drop our own deterrent in these uncertain times. The major reason there has been little action taken over the sinking of the Cheyhan (spelling?) is that North Korea possess nuclear weapons. Should Iran start acting in this manner would we really want to be in a position where we could not fight fire with fire? All the conventional forces in the world are no good when they could lob a nuclear weapon at the UK in response. If we give this up it will take decades to re-establish. When world events are changed over the course of days and weeks that is an unacceptable risk.
Finally, there is the political status of the UK. Giving up the nuclear weapons would de-legitimise ourselves as a world power. Of course, we are not as significant as we once were, but are still regarded as a major player. By stepping back from the nuclear club and accepting that we are not prepared to meet the cost of guaranteeing our own security means we cannot guarantee anyone else's. I doubt Cameron would want to be remembered for such a backward step.
In Summary, I respect people's view about not wanting to renew Trident, or scaling it back etc. However all of these arguments have far stronger counter arguments to them. The only factor that has made this an issue now is money. If our security depends on a choice of funding Afghanistan, of a Trident successor - it is a no-brainer.
I think that is the real decision Osborne is trying to force Fox to make.
I suspect the pace of the decision is being dictated by the desire to start SSBN replacement at the end of the Astute production line (to keep the drumbeat going). Slow down the pace of the Astute builds and you could delay a replacement decision for another 5 years minimum (at least until the end of Trident's expected life end in 2030). Hopefully we'd have some cash then AND the threat from new nuclear states would by that time be scary enough to persuade both politicians and public that this isn't something we can afford not to have.
