They want decisive and ambitious action, you can't get that if we all turn to doomerism.
Now that we've established that, what's your decisive and ambitious action you've made towards addressing climate change, so we can learn from the example you've set?
I'd also probably agree that there is likely misguided opposition to it as a tool in the climate change arsenal as well from "climate advocates" (taboo). The same could also be said for fission nuclear power which, unlike SO2 geoengineering, would substantially address the root cause of the problem - emissions - with fewer risks and unknowns. (France, for example, being a real-world example of how many countries could almost completely decarbonize their electric generation in a proven and scalable way with nuclear fission.)
If we further broaden our scope of misguided opposition from just "climate advocates" to voting polities in countries that are positioned to meaningfully address climate change at a global scale, then we're really getting to the root of the issue. The single most impactful action the average person could take to fight climate change in the US is to vote blue. It's an effectively binary choice to give badly-needed societal support and investment to climate-relevant initiatives like your friends' and so many others.
anyway my model is: we just have to survive a few years before Wright’s Law pushes solar+batteries so cheap that fossil is priced out of the market. Thus aerosol injection to bridge the gap until drawdown