We already are performing geoengineering on the Earth, as you point out. We can't not do geoengineering anymore. Either we can continue the geoengineering we have been doing, or change the geoengineering to work towards some other goal, but there isn't an option where we don't do geoengineering. If you are driving a car towards what you think might be a cliff, you can't choose not to drive. You can continue driving the way you are, you can turn, you can brake, but you can't not drive.
Anything we choose to do will require geoengineering. We can continue dumping CO2 into the air, which is geoengineering. We can try to make our atmosphere more reflective, which is geoengineering. We can try to pull carbon out of the atmosphere, which is geoengineering. We can try to completely stop putting CO2 in the air, which is geoengineering. We need to change the state of Earth, which, pretty much by definition, is geoengineering.
Anything we choose to do will require geoengineering. We can continue dumping CO2 into the air, which is geoengineering. We can try to make our atmosphere more reflective, which is geoengineering. We can try to pull carbon out of the atmosphere, which is geoengineering. We can try to completely stop putting CO2 in the air, which is geoengineering. We need to change the state of Earth, which, pretty much by definition, is geoengineering.