You are assuming your enemy will be a rational one.
The thing is this, if we get nukes here, what is to stop our
potential enemies from getting their own? Pandora's box would
already have been opened.
Another thing to consider, what if your enemy was fanatical enough
to be willing to take one or two nukes in exchange for landing one
one you?
Will Singapore be able to take one nuke hit? No.
Will other countries need more then one nuke to totally take out?
Yes.
When it comes to WMD, it is a lose-lose situtation for Singapore.
We will have no bargaining chips, if we do not have a conventional
army. Don't have to talk about invasion... a potential enemy does
not need to force you to last resort, there are plenty of ways to
skin a cat.
They can simply blockade us and cut off our sea lanes, without a
navy to respond and enforce our side of the sea, we are pretty much
screwed. They can do plenty of things to us if we do not have a
conventional army. They can wage sustained Low-Intensity-Conflict
on us and we will be pretty much helpless. As long as they don't
cross the line, they can mess with us pretty much all they want
because the only thing we have is a nuke and we can't pretty much
us it until things are really bad... but they can make it bad
enough without ever crossing the line.
And frankly no nation on the world will look kindly on us if we
threaten tonuke anybody for the slightest thing, some things still
need to be settled with grunt work and show of conventional
force.
If we dump our conventional forces and just take up nukes, rest
assured, you will suddenly realize that Singapore has no bargaining
chips in international politics.