"The tech" is so far beyond what we can do that we would have self-contained cities in the Gobi desert, on Antarctica, and likely underwater and underground too, long before we can think of terraforming Mars. Even a dinosaur killer wouldn't be enough, while a supernova explosion like the one proposed as the trigger for the Devonian and Ordovician extinction events would also affect Mars.
As others have long pointed out, the population on Mars would need to be in the hundreds of millions just to have enough people with enough specializations to build and maintain the the equipment, and train those people, and the medical staff who take care of them, and the caregivers who raise the babies, along with the farmers, and plumbers, and everyone else. See https://www.antipope.org/charlie/blog-static/2010/07/insuffi... .
Or we hand-wave and say the tech is so advanced that computers do everything, in which case, why Mars when the magic tech can let humans live anywhere?