Ask HN: Does the concept of karma(rating of users) essential for social networks

I have the idea of building a new social website which will basically rely on user generated content and I have the ultimate debate in my mind for a quite long time if I should have some sort of "rating of users".

You may think of the idea of my website very similar to Redddit. Users will be contributing the website and the content provided will be shared among the community. In such communities what is the real purpose of having karma-based systems. I cannot think objectively.

For example:

- Does it help encouraging people to add more content?

- Does it help encouraging people to add more "quality" content?

- Does it discourage people if they encounter with negative comments?

- Does it help user loyalty?

- Is it sufficient enough to rely on such karma-based system where users rate each others content to find out the better content? Or it could be misleading?

- Does these rules apply everybody?

Please think of rating of users in every possible way. Up votes, thanks, likes, retweets.