It is more important to colonize Mars than to solve problems at home, because colonizing Mars will make us marvel at what people can do. Solving problems at home is usually turning our wheels. We cannot solve poverty by throwing money at it. But we can put a man on Mars.
Habitat not completely self contained - e.g. Maybe you need to dispose of human wastes outside the habitat - or some chemical builds up which needs to be vented to the exterior.
Spacesuits leak - the problem is - that the more flexible the spacesuit, then the more joints it has, and these continuously leak air. Could you contain micro-organisms within the spacesuit without them leaking out of the joints?
Airlock - it may be possible to do something about this, but no-one has yet designed an airlock that vents no air at all out of the spaceship. The suit port gets close to this, but is designed more to prevent dust getting into the cabin than to prevent air getting out. Some air would still escape, about a cubic foot in the current design of the suit port.
Accidents - e.g. Spacesuit breached in an accident on th surface. Or one of th spaceships crashes during landing. Even if crew survive, the hull may be breached and contaminate Mars with the micro-organisms inside the habitat. If anyone dies, then that is a major contamination right away.
I definitely think that solving problems at home are more important than trying to colonize mars. While it would be an amazing thing to try and inhabit mars, I do not think that it outweighs trying to fix all the problems and issues we have here in our home planet.
We will likely put a man on mars, however colonizing it for long term use is very difficult. There is a good chance for a large scale failure of a colony on mars, which would be throwing millions of dollars down the drain. We should make sure our home is able to be sustainable before we try to make sustained life thousands of miles away
Although colonizing Mars needs to be a priority, there are many problems at home that need to be solved before extra resources can be focused on space exploration and colonization. Education, social equality, and care for the poor and less fortunate need to be higher on the priority list than heading to Mars.
Colonizing Mars sounds fascinating and I think it's something we should try to do, but maybe in the future. Why not try and create technology that can provide faster travel in space before colonizing a planet so far away. I think if the funds were to go to one or the other, we should certainly focus on solving our problems at home. The United States government is broken and needs serious repair.