Most movies made today should and can be streamed on the date of the release. They are filmed digitally and look the same on a movie screen as they do in the theater. However, if a film is produced in a way that warrants it, it should only be released in the theater first. For example, films shot on film and are run by a projector.
I know that some believe that it would hurt the movie theaters if this happened. But I tend to disagree, some individuals like to go to the movies to have experience of sitting the theater. Also, if the movie is put online and a person likes it enough thy could want to go see it in the theater to see it on the big screen. So in a way putting it online could be another promotion.
Movies should be released online the same time as they are released in theaters because theatergoers are different than people who prefer to watch movies at home. Going to the movies and watching a film in theaters is an experience and not just about seeing the movie. People who like to go to the movies are not likely to stop going just because they can also buy it online, and people who want to get it online also won't have to wait for everyone to see it before them.
Releasing movies online and in theaters at the same time would wreck the pricing/profit model of the movie industry. It would result in few big screen feature movies being made since there would be less profit generated from the big screen showing of movies. It could even possible drive up the costs for in-home viewing of movies.