I am planning to have a website where I shall post links to user profiles from Facebook and LInkedIn categorized according to their geographies, interests, profession etc. Are there any legal issues with that ? Since the profile is public anyway and the information that I will be able to access, will be made available to me only after the users allow my FB app to do so. If a user has accepted to allow my FB app to access those information, is it legally wrong to show that information on my site ?
Even if it's legal, is it ethical?
Do you wish to have a business based on people information from people that have not agreed with you publishing their information?
As you've stated, even some FB apps do request your permission to access your information, how would you feel if someone publish your information, even if it's public, on their site?
My advice, you should get their permission before publishing their information. Otherwise you may become persona non grata among users.
It would not be illegal nor against the terms of service of most social sites (Twitter, Facebook, G+) to display user information including demographics and profile details if you get the user's explicit consent to do that. And by "explicit consent" I mean you need to be crystal clear to the user what your intentions are when they sign-up/agree to the service and also include a checkbox or some such mechanism where they agree to your terms.
It would also be a good idea to provide the user quick and easy way of opting out of the service as well.