It would be nice to try to do the right thing even if we might not succeed. The question to my way of thinking is whether we will try, not whether it will work, and the discussion should be about what the actual consequences would be and the best and safest (most conservative) way forward.
There are real risks to remaining dependent on fossil fuels (a limited resource) and foreign fossil fuels (bargaining chip for hostile countries). There are risks to switching to sustainables (economic, perhaps, etc)
I am a strong proponent of solar, everyone agrees that warming is due to solar radiation, so it should be obvious that the sun is hitting us with us tons of energy every day. But we don't know the environmental costs of generating the panels, etc, so a balanced portfolio including remaining on fossil fuels while other risks are determined from sustainables, seems reasonable.
But, not doing anything, seems like we are defeatist.