Remember, part of demand is the amount people are willing and able to pay.
Overall, I'd argue that by increasing a person's ability to pay for anything you increase their ability to walk away from all kinds of bad deals. One of the best examples of this is given by Terry Pratchett:
The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.
Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.
But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that'd still be keeping his feet dry in ten years' time, while the poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.
This was the Captain Samuel Vimes 'Boots' theory of socioeconomic unfairness.
A beef carcass might have 500 pounds of meat on it, but only 5-10lbs of that is tenderloin. If we all have enough money to buy tenderloin it doesn't immediately follow that cows are then made up of nothing but tenderloin. So the price of tenderloin will go up until the demand balances the supply again. You can take this and apply it nearly anywhere in the economy and find it'll be approximately correct for a great many situations.
And there's the rub. Even if we could make 500lb all-tenderloin cattle you wouldn't see people buying hundreds of pounds of beef tenderloin for themselves every day. Billionaries like Bill Gates can already afford millions of pounds of tenderloin yet you don't see him eating that.
Basic income might cause the price of tenderloin to go up a little bit but so what? It's not going to do anything to the price of corn or rice or wheat. Maybe the price of an apartment in Manhattan will go up a little bit (I doubt it) but not a house in rural Wisconsin.
