Can't touch on everything since I am at work, but did you even read what you posted? Note that is is not the only instance of radiometric dating giving the wrong dates, but their 2 defenses against the argon present in the sample are 1) leftover argon from previous experiments in the equipment (of course they don't Iquestion this when the dates agree with their pre-conceptions) and 2) excess argon was present because not all argon leaves when lava forms (this would question all other dates obtained by the method). Excess argon is a real problem for geologists to explain.
Not only that, but their argument against the experiment itself is that you can't use this method to date anything less than 10,000 years old. So yes, they have to assume that it is old from the beginning. If all samples were indeed "young", and contained argon, they would still yield the millions and billions of years that geologists want to find. It's not that a few instances make us question the entire method... it's that when we can actually observe initial ratios of argon, it defies the ASSUMPTION that old lava started with no argon. When the dates disagree with the preconceived assumptions, they are discarded as errors.