For starters it's too cold, too dry, atmosphere is too thin, and there's no reasonably sustainable power source.
But all of that is irrelevant because there's no magnetic field. So radiation. So unlivable.
There's also no point in a colony there. If life ends on earth it ends on Mars. There are no materials there we want. It offers exactly nothing we can't do better here, for much less money.
Will we land on Mars? Sure. There's always the goal of being first. But live there? No. Unsupported by earth? Very much no.