You can chage these activites if you are not happy with them. Go to Tools > Options. Go to the Advanced tab. One th bottom part of the window, there is a small section called "Connection Preferencing." If you have 1 or higher in the input field AND/OR have your Allow Freeloaders slider at Rarely, then your uploads will be unsuccessful to varying degrees.

I would really recommend making sure that your settings are active so as to preserve the existing integrity of the network. If people who don't share files (freeloaders) are taking up all of your bandwidth, someone who is actually sharing files will not be able to get anything from you. People who actually contribute to the network's content should have the first priority. :-)