Let me continue the list:

7. That what was reported to them through the news media was taken for truth

8. That entertainment was glorified as of paramount importance and fame was worshipped.

9. That beauty was mistaken for goodness

I love #6's answer! I will add to his list:

4. That entertainment was considered as a passive activity that people sat and had done to them.

5. That one gender is somehow inferior to the other.

6. That people could totally neglect the health of their bodies and then expects others, known as doctors, to fix all they damage they had done to themselves with that neglect.

Looking back, as someone already pointed out, is a good model for trying to figure out what once seemed reasonable but now seems rather outlandish and for predicting the things in our current culture which will be looked at in the same way by future generations. 

I agree with the above post that the people we glorify (as measured by how much we pay them and/or the license they have for bad behavior) will seem ridiculous one day.

Unfortunately, I fear that the traditional American work ethic will one day seem silly.

Reality television and the idea that we can be entertained by artificial competitions in a variety of increasingly outrageous settings and challenges is going to make us look foolish and puerile.

1. That television and iPhones could have been so addictive that people spent the better part of their days mesmerized by them.
2. That we allowed the oil industry to control the world's financial structure.
3. That sports figures became the dominant "heroes" of American society.

I think national identity, at least as we think of it now, might be obsolete in the distant future, and that people will wonder why we felt so strongly about nation that some people were willing to die for it. Ideas of nation barely existed 400 years ago, and there is every chance that they might be a thing of the past before too long, historically speaking.

If history is any indicator or understanding of medicine and science should advance to a point to where our technology and treatments would seem extremely elementary.  We are unable to cure or effectively treat a multitude of diseases, and if those can be cured in the future I am certain our methods would seem childish.

One might be the belief that there are inherent differences between people of different races.  We're already losing this one to some degree.  Another might be that homosexuality is in some way evil or immoral.  I suppose it is possible that one day people will also think we were silly for thinking that men and women are inherently different in terms of mental capacity or emotional natures.  

There are many ancient beliefs and superstitions that ancient civilizations had we consider comical today. These beliefs have been “revealed” to be natural or scientific phenomenon, but many years ago their exact cause was misunderstood.

One such belief was that most maritime disasters today are caused by navigation errors or weather phenomena. In early times, most maritime disasters involving lost ships and crew were the result of sea monster attacks. Ancient mariners believed that if you wandered too far away from the shore your ship could run afoul of large creatures, which would consume it and your crewmates. 

Another common one involves people today who are left-handed. Today, we know that your left or right-handedness is not a comment on your personality. In some Christian societies people who wrote with their left hand instead of the right hand were possessed by the devil. In Puritan New England parents would often strap their children’s left hand across their chest to prevent them from using their “bad hand” if they exhibited tendencies. Because being possessed was such a dangerous thing in the New England colonies, many people would even whip their children to prevent them from using their left hand.  

A final superstition from back in history involves the weather. Today we know that natural disasters are caused by weather and tectonic factors causing natural disasters. In ancient times the commonly held belief was that natural disasters, such as famine, earthquakes or hurricanes were the gods showing their displeasure over people’s behaviors. Many civilizations across the world shared this belief and incorporated it into their religion, such as the Greeks, Native Americans, and Ancient African cultures.