It depends upon what shows someone watches, but television can and does brainwash us. Many people who watch Fox News don't understand that it is propaganda and repeat it's talking points everywhere they go. Also, commercials are effective in getting people to buy their products. If they were not effective, companies wouldn't continue to spend money on them.
Yes, television is brainwashing us, because it makes us act like the people on television. People see ads on television and start to think they have to have the things that are advertised. This is why it is expensive to live in the United States, despite our very high standard of living. People are too easily swayed by what they see.
I believe that television programming often aims to push the envelope as to what is acceptable and not acceptable in society. What is seen on TV is generally not accepted in society, but the more it's seen, the more people begin to accept it. Often, this is done through humor or through exaggerated behaviors. As we watch these again and again, we can become desensitized to them--things like violence, swearing, and other behaviors that our grandparents would have raised their eyebrows over. We can see this even in the influence certain shows, like Mad Men, have had on fashion and in other areas of our lives. Some people likely don't mind how television is changing society through its exaggerations of everyday life, but others will see it as a negative aspect of TV.