If you have a website where users 90% of time only read and view content, but rarely post, like a blog, does it make sense to force a login?

If I force the user to login to view some information, like how Quora.com lets you only view the 1st answer unless you log in, will this turn people away? Especially if other sites offering content close to yours don't force logins?

The advantages of a forced login are 2:

• you know exactly who your user is and you can design your website according to user's behavior and
• you can keep scrapers away much easier, especially if you hide the content scrapers want.

Generally, are people sick of logins?