It's far too simplistic to blame speculators - I think you've vastly over-estimated their influence. The price rise in oil is causing speculative interest, not the other way around.
Your argument doesn't work when you compare other commodities. Take Nickel, for instance, which has had a flow of investment over past year comparable to that of oil - and the price has dropped.
You could also compare Cadmium, which has grown even faster than oil over the past few years with relatively little investment or speculation.
Ergo, there isn't actually a consistent and clear correlation between speculation and commodity price.You have to remember that speculators essentially bet on how prices are going to go - in the case of oil, they were allready going up.
buy and sell things that they dont even own (or want) to make money.
Futures are essentially just contracts promising future delivery, so in fact they're just bascially trading (or, rather, promising to) but hoping to secure a contract at today's rates which hopefully (certainly in the case of oil) in the future will save money because the price is going up. I don't see that anyone's being robbed.
Also, I can't see any concrete evidence in your first link that speculators are causing the food price increases so much as just betting on them.