I disagree. The advantages of earlier colonization are considerable in terms of the level of interest that would be maintained, not to mention getting started while there is still interest and before something goes wrong here. Martians would care a whole lot more about solving the terraforming problems than we do back here. They would also be far less vulnerable to political whims and fads than we are. It's easy for our morons to whine that we should feed our hungry before we provide any funds for Mars, even though we can never feed all the hungry because of the choices they make. It's almost unimaginable that Martian colonists would take the same attitude.
I'd like to go to Mars as soon as we are ready, with people staying there and building a self-sustaining civilization. If we do it with people over 45 or 50 years old, so that they already have kids grown and out of the house, they can build without worrying as much about whether their children are in danger, and that might be a compromise from true colonization. However, I like the idea of building for my children. If we had a mission in two years, I'd be training, studying, and getting in shape to qualify and encouraging perhaps half of my children to come along.
Despite what Zubrin has claimed for years, terraforming Mars — using ‘greenhouse gases’ btw — will be an enormous project, will have to involve introduced gases, and the impact won’t be felt for a long, long time — length of a human lifetime or more. Dropping big blobs of frozen gas will be non-trivial impacts, especially at first, and will have the additional benefit of pulverizing the hard surface of the planet.