No! It's malware. Do not download.
Guys, MacKeeper is a legit app - visit its official website mackeeper.com to make sure in it. You can also take a look at the article at Cnet - http://cnet.co/iXiq5s entitled 'How to protect your Mac from recent malware' - MacKeeper is in the list of reputable malware scanners.
You may have mixed up the original app of MacKeeper with MacDefender analogue with the similar title - take a look at the following article at pcfixessupport.com to find out more about that malware - http://bit.ly/izdaxG
As for original MacKeeper, it's easy indeed to uninstall it if you want to - just follow these steps:
1) quit the app
2)drag&drop it to the trash
3) fill in the survey form: just choose one of the reasons why you've decided to uninstall MacKeeper
4) press 'Uninstall' button
and all the components of MacKeeper will be completely removed from your Mac.
You need to type in your pass to delete the app just because it's an action that influences your system. This pass just permits to go on with uninstalling - so you have no need to worry. It's done in order to provide your compute with more safety - one of MacKeeper's tools is Antitheft. So if the MacBook is stolen the thief would be unable to remove the app as he wouldn't know your pass - and it would help to return the computer to its owner.