> What about Gobekli Tepe?
What about it? It's one of the oldest Neolithic settlements we've identified, but otherwise, it's not particularly unusual within our understanding of Neolithic Mesopotamia.
When GP is talking about "material culture", they're (probably) referring to the archaeological definition of culture, which means you need to give an explanation as to what makes an artifact indicative of belonging to a culture. The shape of an arrowhead perhaps, or maybe the kind of style used in painting pottery. Something that lets an archaeologist dig something up and go "aha, this is culture X!" Age isn't one of those characteristics.
But of course the province of pseudoarchaeology is to come up with a theory and work everything into evidence for that theory. Atlantis is old, Göbleki Tepe is old, therefore Göbleki Tepe is Atlantean!
> Skepticism is healthy, but why be dismissive of peoples' interest to consider or search for new evidence? What exactly is the risk?
Most of the people that tend to propose these theories aren't interested in searching for evidence. See for example, Graham Hancock, who has been peddling the same theory for 30 years and has done nothing to actually produce better evidence for it except to whine that mainstream archaeologists don't want to listen to him because they're stuck in their own stupid ways. (Of course, in that same time, mainstream archaeology has thoroughly demolished the Clovis-First hypothesis which was previously disfavored, precisely because the pre-Clovis adherents actually did the legwork to produce better evidence to make it more accepted!) You can also see this with archaeoastronomy, which is borderline fringe--its better practitioners have made some success by listening to the criticisms and persevering in efforts to get better, stronger evidence to buttress their claims. As a basic rule of thumb, if someone's response to criticism is to chide scientists for being rigid in their thinking rather than going out to try to get better evidence, then that's a strong sign they're engaged in pseudoscience and not science.
As for the risk, a lot of these theories bear a deep legacy of overt racism just begin their skin; they've historically been used to devalue the abilities of the people who've made them (e.g., Great Zimbabwe). Nowadays, they've been modified to edit out the basic message of "white people taught everybody how to civilization," so it's no longer quite as overt as their late 19th century ancestors... but you can still see the lingering traces of it in "an ancient civilization taught everybody how to civilization."