I can give you a great example of the positive aspect of speculation.

Look at the futures market. Speculators are a big part of the liquidity of the futures market.

Price of wheat is $60/bushel. Farmer won't harvest for another 6 months and is worried prices will drop. They can secure a future and lock in the price now.

Wheat purchasers aren't on the other side of that trade, because why would they lock in a higher price? A lower price benefits them.

Speculators come in and bet on the price of wheat, creating a deep pool of futures that can be bought and sold.