@FinalPyre
The main scientific reason to colonize Mars is to make it habitable in case Earth becomes unsuitable for life; we can't do that if Mars isn't self-sustaining. If we could build a semi-functioning dome (with current technology), we could theoretically live, but without continuous supplies from Earth, humans would die out.
The only long-term solution is to terraform Mars, or to create a dome that is sufficient for all necessities of life (food, water, oxygen, etc.). Like you said, the problem is that we can't live in a dome without the help of Earth. This renders the entire concept void and somewhat pointless.
And of course, we can't terraform Mars either, so there's currently no way to colonize the planet.