|    High aspect ratio obviously is a good thing, until you look at the negatives.  

I do not see how aspect ratio correlates to knockdown? And you do not actually say it does. Are you suggesting high aspect ratio causes knockdown, and low aspect ratio doesn't? Cause that's just silly.

| On a cat, you have only so much righting moment,

This makes no sense to me. Every boat has finite righting moment. Perhaps we should do a righting moment per dollar comparison.

| and they do NOT come up from a knockdown as a rule.... depending on the degrees
|of the knockdown.  

That is a good point. People should not build cats.

| The other negative is the rate at which the strength and weight must go up on a free standing mast as the height increases.

At what rate is that?

| The leverage is all concentrated against the mast partner.... The longer the handle, the greater the stresses.   

I have heard of knockdowns. Partner failure seems more rare, so this does not seem a concern on most boats. Unless a home builder screws up.

| A monohull has the safety valve of heeling and dumping wind energy by reducing sail area as it heels.

An unstayed mast does something similar to a lesser extent.

| The multihull has far less margin of safety.

You state this as if it is true. I don't think that is true.

|     This of course is all amplified when single handing. 

I don't see how. Safety doesn't change because one is single handed. Perhaps one takes more risks with a crew? But I don't think most cruisers make that choice.

| It's a big factor in how much sail one dares to carry under any given circumstances.

I don't see carrying sails as risk. Hoisting them, as appropriate, makes sense. Having a rig one can depower, or even reef quickly is a safety factor. But the amount of sail aloft seems much less so.

But I know nothing.