I'm no scientist, but I do entertain opposing arguments -- much akin to the scientific method -- and try to consider the whole.
But the arguments have to be valid. Affirming the consequent is an invalid argument.
Scientists are NOT going to make simple logical mistakes as MidiMagic suggested.
Most of the people making these claims are social or environmental scientists. They do not follow the rigor that physical scientists use.
Social and environmental scientists usually can't perform experiments, because they will destroy the only sample they have if they try any experimentation. So they observe and record data, and make conjectures.