If you really wanna dislike people's posts, photos and statuses on Facebook, here is how you can enable it.

Dislike button comes as a Facebook App.

It is a browser add-on letting you dislike stuff on Facebook.

It also add an small ads on the page.

You can download it and install it as follows:

For Firefox Download Here
For Chrome Download Here
For Safari Download Here

Just download, add to you browser and start disliking instantly.
People will ask you how and you shall be happy to tell them how to get it.

FBDislike Home Page: https://www.facebook.com/fdislike