Yes topbunk I agree.
All companies want their pilots to make sensible decisions. The point I was making is that a tonne of fuel is not an awful lot although it may sound it. As we both know many aircraft carry this weight in all sorts of nonsensical ways, such as excess bar/catering, rubbish and even condensation ( although there may be little you can do about the latter). The chances of a diversion become statistically greater the less contingency fuel you carry. The cost of a diversion is rather like "how long is a piece of string", but I would suggest that £3000 - £4000 ($5500 - $7500) would be a reasonably conservative minimum estimate by the time passenger coaching, aircraft delay costs and all the other factors are priced in. Of course it is a theoretical exercise ( since most of us don't put it to the test !) However that would suggest that for an average 2 hour cruise flight sector carrying a tonne of extra fuel ( which I accept may be too much or too little in specific circumstances), the diversion rate would have to be less than 1 in 100 flights (1%) for the mathematics to be in favour of minimum plog fuel.
I know it is difficult to argue any specific cost since we can only apply a broad brush to the whole matter, but I would maintain that is food for though and I believe the figures I have used are probably erring on the lower side as regards the diversion costs.