As one of those environmentalists, my qualm isn't so much that this may be dangerous but that carbon capture tech (and associated "carbon capture and storage") is often championed by people looking to delay implementation of technology and laws that limit carbon emissions. It is far more energy-efficient to curtail carbon emissions than try to capture it once emitted. The most efficient use of money is to do things like close coal power plants in favor of solar/wind. Once all the coal plants are gone, then is the time to focus on capture.
