Yes, that's all true. But I've also never heard a plausible argument against the simple observation that if I kick a football it will accelerate away from me. F=ma and all that... Unless I'm standing at the bottom of a hill, in which case it will roll straight back to my feet. See, the wider system may be more complex, and have negative feedbacks that overwhelm any perturbation you introduce. The onus is on the climate scientists to show that the system as a whole will behave as they've predicted, which is a great deal trickier than your simple observation... since it's just about the most complex system imaginable. I model for a living, and I'd dead-set rather model the human brain than the climate of our entire planet. At least you've got 6 billion of those to gather data on. Or experiment on. They've got one.