Ironically we don't produce enough CO2 (in concentrated form) to do that on a large scale. This means that we might have to use direct air capture to get the CO2, which is quite expensive. It also begs the question: Since the CO2 is going to end up in the atmosphere anyway, then why go atmosphere -> CO2 -> synfuel -> atmosphere instead of fossil fuel -> atmosphere AND atmosphere -> CO2 -> underground storage. The second might be cheaper and the end result in terms of CO2 in the atmosphere will be the same.