Re: I want to know the salary rang
You have made the faulty assumption that you are paid, or should be paid, according to your worth to the company.
Lets turn this around and you are doing the hiring, looking for someone to do work for you (paint your house, fix your driveway, whatever). You put together the requirements and you have a general idea what you are willing to pay, but you don't necessarily tell the prospective bidders what that amount would be.
You may interview multiple people or companies, and receive several bids. In the end, you accept the lowest bid that covers all of your requirements, or you adjust your requirements in order to get something that falls within your budget.
Nobody thinks that doing this is "unfair", they see it as getting the best value for the money and not overpaying -- yet somehow when those roles are reversed they complain.
The reality is that the job is only worth what the lowest bidder is willing to take. It is the same process whether you are the job applicant, the company hiring for a new position, or the company selling its services to another.