At the same time, the physics dictate that the general sign and order of magnitude of CO2 forcing in climate models is correct, as surely as doubling solar output would increase mean surface temperatures. The physics also don't preclude the effects being even more severe than the models predict. But there's considerable uncertainty involved in both directions, and when people hear "well, things might end up better than scientists think is the average case, and at no cost to us!" they jump for that option and ignore the average prediction, let alone the worst case scenario that's within plausibility.
Coupled with an extremely well-funded group of fossil fuel industrialists putting hundreds of millions of dollars into the outright shutting down of climate research, good scientists and especially not-at-all-scientific activists end up on the defensive, overemphasizing the finality of the models and using them as solid predictions instead of tools to vindicate the general thrust of the physics.
As far as your particular point, think of the the models in climate journals as tools to understand the issue instead of the final word. It is somewhere between very difficult and impossible to come up with a climate model where CO2 forcing doesn't cause significant warming, but individual parts of those models need to be and often are tested. Indeed, those are the main points of dispute in the legitimate research and end up being thoroughly vetted.