This is incredibly poor thinking.
You're assuming that the risk of doing nothing and suffering 4-6 degrees of warming is somehow equivalent to the risk of taking some action to mitigate the worst (but not all) effects of that warming. Clearly there are significant unknowns to the aerosol approach to solar geoengineering, which is why we should strive to learn more about it, not dismiss it out of hand.
You talk about 4-6 degrees of warming like its somehow a linear progression from the 1+ degree we're experiencing now. However, that's hardly the case. 4-6 degrees will fundamentally restructure agriculture, fresh water distribution, habitable population areas, and innumerable other things. Modern civilization depends on an extraordinarily complex interrelationship of economic flows, supply chains, and necessities that have finite elasticity and resilience. Already in California, where a huge fraction of America's fresh produce comes from, we're experiencing record droughts, and are looking at major impacts to agriculture. What will 4-6 degrees add to that? Would you like to sit around and wait to find out?
What you're suggesting here is that we roll our dice and take the worst of what's coming without considering any mitigating action-- simply because of the chance that we might not be able to continue to pursue that mitigation. That's the same as saying "I won't go on dialysis, because it's possible I might not be able to continue." But you go on dialysis because you don't have any other options-- and you take your chances from there.