There are still some people who feel that mars can be habitable simply because it has some features that are similar to earth. Take note that it can only be habitable if there would be some mechanisms and technologies that will be installed. The surface and the atmosphere of Mars is very much different from that of the earth.
One of the greatest challenges about living on Mars is the low gravitational pull. There is a chance that the items may not completely stay in place even when they are placed there. Some say that it may have been more habitable in the past but it has lost its atmosphere and changed the condition of the whole planet.