Doing solar radiation management as a substitute for drawing down CO2 would be disastrous.

But we're starting to see various positive feedbacks kick in, where rising temperatures cause the planet to release CO2 and methane of its own. We see evidence of this in geologic history too, where a modest temperature increase due to an orbital variation causes greenhouse releases that tip the planet into a warming cycle.

If we cross that tipping point, reducing our emissions to zero won't keep the CO2 from increasing further. We might need SRM to keep that from happening. The tipping point could be as low as +1.5C, we're already over +1C, and we've made essentially zero reductions to our emissions so far.