Whether it is constant or not, that can be debatable.
Sure it can be debatable. If the evidence for a constant decay rate were equivocal then the conclusion that the decay rate is constant would be debatable. But the evidence for a constant decay rate is unequivocal. Even the RATE group discovered that it is unequivocal.
In case it wasn't clear from Coyote's post, the RATE project was a creationist research effort conducted under the auspices of the Institute for Creation Research and the Creation Research Society.