Why is radiocarbon dating unreliable as proof of an old earth?

Radiocarbon dating only goes back to about fifty thousand years, possibly a hundred thousand in rare cases, so it cannot even reach the two or three hundred thousand years evolutionists claim for man. Like stellar parallax, the readings that are good are the ones relatively close in; the good radiocarbon dates are roughly ten thousand to thirty thousand years, and even then we question them, because we cannot prove that the decay rate of carbon-14 to nitrogen-14 has been constant. Evolutionists need a uniformitarian environment, but if anything catastrophic altered the decay rate, everything is thrown wide open. When they took potassium-argon samples from Mount St. Helens, whose lava was only a couple of years old, they got readings of one to two million years, so something is wrong. And they keep finding soft tissue in dinosaur bones; Mary Schweitzer found blood cells, blood vessels, and collagen inside a T. rex femur, which could not survive if the bone were sixty-five million years old. So you take every radiocarbon date with a grain of salt.