They're Jews, you may as well as water to stop being wet.
>is there any reason other than to deprive the individual of his well earned money or what moral purposes do banks need for that extra money? It's not theirs.
You understand the concept of time-preference, yes? The notion that, other things equal, any one of us would prefer $100 nw over the same $100 a year from now? Therefore, it may be said that the $100 right now is more valuable than $100 a year from now. If something is valuable, then logically people are willing to pay a price for it, and logically people who own the valuable thing will demand a price for it. And that's all an interest rate is, is a price. You want X amount of money now instead of a year from now, so you're willing to pay a certain premium to get X now, even though you could get X without paying the premium if you put part of your income aside for a year. But for whatever reason you won't or can't wait that long, so instead of waiting you pay that price. And of course, the bank takes a bit of profit because they went through all the trouble of making sure they have money to give you right now, all gathered in one place so that you can get your loan near-instantly. You could probably go around to all your friends and family, and gather up a few dollars here, a few there, and promise to pay them all back at this interest rate or that interest rate, but that costs a lot of time and effort on your part. For not expending that time and effort, you're willing to pay the bank a premium for organizing everything, and charging you a single rate instead of a dozen different ones. It's no more exploitive than it is exploitive for a restaurant to charge you more than the material cost of the ingredients when you order food.
People give their money to banks voluntarily. They also take out loans voluntarily, and voluntarily pay that interest. If interest rates are so exploitive, why do people do these things of their own accord?
>why would people have jobs in first place when they could sit around speculating the stock exchange if it's more profitable?
This is a lot like asking, "why would anyone flip burgers if going into carpentry is more profitable?" For starters, people have different skills, different abilities, and different preferences. Not everyone has the skill to speculate on the stock market. Of those that do have the skill, a lot have even higher skill in some other area, meaning it's more profitable for them to go into another field. Of those that do have the skill for day trading and do it well, a lot will go into another field simply because they hate the idea of sitting inside staring at stock prices all day more than they like the extra income they'd gain from doing so.
But more to the point, even if we ignore the skill and preference barriers to day-trading, there's a natural cap on how many people will engage in it through the nature of arbitrage. All profit on the stock market (all profit everywhere really, but that's not what we're discussing) is acquired through finding and exploiting opportunities of arbitrage–buying low and selling high. This could be buying in a "low" area and selling in a "high" one, buying during a "low" time period and selling when the price is high, or any other combination you can imagine. The fewer people there are exploiting arbitrage opportunities, the more profitable it is. With fewer people, arbitrage opportunities are open for longer–the length of time before the two prices equalize is longer–and they are more dramatic–the difference between the high price and the low price is larger. If a lot of people are exploiting arbitrage opportunities, they're open for a much shorter period of time, because when you buy in the low area, you decrease the supply (thus raising the price a bit), and when you sell in the high area you increase the supply (thus lowering the price a bit). If there are more people buying and selling, this equalization happens a lot faster. And once the major arbitrage opportunities are equalized, investors have to look for much smaller ones just to make a profit. What this means is that the more people there are speculating, the less profit any one person will get. At a certain point, the profit from speculating is small enough that people move away from it and towards other methods of profit, such as a regular job. This effect holds in some way or another in all industries, and not just for businessowners, but for laborers as well. It's one of the mechanisms that naturally prevents resources from being dumped into any one area of the economy, and are instead diverted to where they are needed most.