The first sentence is true. But it’s irrelevant to this discussion, unless you misspelled “scientists”, in which case none of what you said makes any sense and contravenes the fundamental principles of science. This misspelling of “scientists” as “advocates” is very annoying, as if every climate scientist was a charter member of Greenpeace by profession instead of actually being, you know, a researcher in a scientific discipline.
The problem with any incompetent amateur armchair analysis of scientific evidence is that it is, by definition, amateur and uninformed, and if said incompetent also has a self-interested preconceived opinion, then the resultant conclusions will generally be wrong. That’s why we rely on scientists for scientific advice, and doctors for medical advice, and engineers for engineering advice.
The argument against “climate models” is beyond absurd – it’s at the level of “not even wrong”, just stupid. There’s no such monolithic entity as “a” climate model. There are everything from simple energy balance models right up to coupled atmosphere-ocean global circulation models and comprehensive earth system models; there are weather models, and short-term climate models, and long-term climate models; there are finely grained regional models and large-scale models and global models. What models do the denialists think are “wrong”? In what respect – temperature projections, sea level rise, ice melt or ice cover projections, vegetation change projections, or any of the hundreds of other factors?
Specific critiques of specific model behaviors invariably turn out to be misleading as already noted about the arguments cited by the OP. It’s based on the tired old tradition of implicitly assuming that a complex subject is actually very simple, presenting some misleading and simplistically simple piece of evidence as an apparent flaw, and then letting stupid armchair analysts reach stupid conclusions – the same armchair analysts that have no problem at all relying on science and medicine for expert guidance in areas where they don’t have a vested interest.
The short answer to it all is that climate models build up simulations from physical basics about which there is no doubt whatsoever, such as the forcing that is imposed on the climate system by every increment of CO2, which is given by the CO2 radiative transfer code, and which is at levels unprecedented in millions of years. There is no doubt about the rapid melting of the Arctic and the general loss of ice mass in the Antarctic, the rise of sea levels, and record global annual temperatures being set year after year.
It gets more complex when factoring in how large-scale feedbacks – mostly positive ones but some negative ones, too – affect the net global climate forcing. It gets still more complex when trying to relate the net forcing to projections of global temperature change in any particular timeframe, or with global circulation changes or hundreds of other physical manifestations that are modeled in climate simulations, but some of those destabilizations are associated with subjectively small temperature changes and many are already being observed, like significant precipitation anomalies. But the uncertainties in more specific projections should never obscure the fact that present CO2 concentrations and directly observable changes in the earth’s energy balance are completely unprecedented in human history and pose a serious threat to the stability of the climate system.