Yes, the dangers associated with travel to Mars far outweigh any benefit that may accrue from a manned mission. Until space travel to the Moon has been perfected I don't believe it is in the interest of science to embark on a hazardous mission that is more 'boy's own' fiction than fact. The failure of such a high profile mission could set back space exploration for decades. It is somewhat understandable that the recent successful landing on the Red planet has made a manned landing more attractive in the minds of many star gazers but it would be foolish for the scientific community to get carried away by such limited accomplishments.
The forays to Mars so far have not been unqualified successes. One crashed without trace, another safely landed but was apparently too damaged to send back any data. The only successful manned capsule re-entries to Earth have been where the capsule has not been required again for re-use. The Martian gravity is much stronger than the moon's and so the terminal velocity on Mars will be much higher leading to a higher impact landing. There is always the chance that some components could be irreparably damaged in any attempt. The first step in building confidence for a manned mission would be trying to get one of these Martian landers back to Earth.
The physical effects of weightlessness on the human body are understood enough at present for us to know that if astronauts reached Mars there would be no Neil Armstrong moment where the capsule pilot bounds down the ladder to claim Mars for mankind. After months of bone decaying travel the pilots would be incapacitated in their module for days or maybe weeks reacclimatising to the Martian gravity. What is not understood and can not be pre-determined will be the psychological effects on such isolated travel. Even the simplest of situations can be major life or death struggles in space; food poisoning that rendered the crew helpless could jeopardize their safety. Apart from the human tragedy of any potential crisis the worst PR ever would be the knowledge that astronauts were dying in space while ground crew watched on impotently.
For the scientific community the priority has to be on setting up a habitable base camp on the Moon. From this platform it would be easier to launch a larger spaceship with a greater payload. This is essential to ensure that the astronauts will have sufficient provisions and built-in redundancy in their system to tackle any unforeseen events. The other moral question is how any country could justify such speculative spending, of limited scientific value to mankind, when there are so much more pressing problems to be addressed here on Earth.