High sugar intake weakens your immune system, and is inflammatory.
Citation required. For both claims.
Maybe for the first one, but if you read even a little into how your diet affects the body then you should know that sugar is inflammatory.. but here you go
Effect of various carbohydrates on immune system. This shows that ingesting sugar weakens your immune system, and that fasting actually boosts it (which may be a reason that we sometimes lose our appetite when we're sick).
Sugar and inflammation. Though if you wanted, you could just try it yourself. Increasing your sugar intake also causes your body to retain more water and salt.
Given that most of the food i have still goes off, clearly its less preserving than your assertion.
Does most of the food that you have also contain artificial preservatives? I doubt it. I have to avoid sulphites. They're found in pretty much all wine, some beers (anything German is usually fine thanks to the Reinheitsgebot), cider, dried fruits, glucose syrup, any processed corn ingredient (maize starch, corn flour, HFCS, etc), and more..