I don't think I've ever seen anyone here insist that lizards have actually interbred with humans. I've seen lots of people claim the notion as a metaphor, though.
I can understand how there can be value in considering Icke's reptillian theories. There are people in the world whose actions and motivations seem at first glance so incongruous with simple notions of normative behavior as to be unimaginable as human. Slaughtering millions, creating vast death zones, plainly enjoying the fruits of exploitation and disease, preying upon the weakest for a percentage... you know, those kinds of things. And so we search for what is different about them in order to divorce ourselves from them. They are called by some, reptilian, or, more meaningfully, sociopathic.
The typical targets of the term - European royal houses, zionist elites (

), banking cartels, politicians, and business executives all exist at a far enough social and economic distance from the average followers of Icke's theory to be all but invisible to them, and that makes them both difficult to psychoanalyze and easy to stereotype and label. But any attempt to deprive them of their humanness is fucked up.
Is the theory as dangerous as belief in presence of Satan incarnate in those you would hate? No. Is it as dangerous as being a republican? No. Is it as dangerous as espousing intelligent design in schools? No. Is it as dangerous as misogyny? No. Is it as dangerous as unfettered capitalism? No. A toddler with a pistol? Bathrooms without non-slip tiles? Pleated pants? No, no, no. And so, so, very on. But the line between literary metaphor and pseudo-history has been sufficiently blurred by Icke as to allow for a degree of counterproductive dehumanization.
But he's no more dangerous than any number of fairy tales or creation myths floating around. If you don't like his mythos, there are plenty of others equally weird, and far more provocative to deal with. Christianity, for instance.
I believe there are presences and forces in the world that are outside of the finality of scientific discovery and explanation. I believe this because I have experienced them myself. In Icke's followers, his adamant purveyors of orthodoxy, there is a group which contends to have such first-hand experience of the reptilians. They have literally seen it. Icke himself claims to have been subject to a epiphantic vision. So who am I to dispute what their eyes have told them is the truth? But that is different from the supposition of a vast network of aliens invisibly running the planet's elite as interpreted through readings of ancient religious tracts, and working to separate yourself in kind from those you might call "the reptiles" because of their actions.
It takes a certain kind of naiveté to sufficiently divorce sociopathic behaviors from humanity to believe that a real, actual, slavering, scaly-skinned, fourth-dimensional lizard hybrid might be responsible rather than the flesh and blood, non-shapeshifting persons widely known to us. The people responsible for the horrors of history, or for the exploitation of the world today, are not special. They are not endowed with powers from another world. They are, in fact, lacking a certain power granted to most of us. Empathy.
But even as a metaphor, I can't understand how there can be a great deal of value in considering Icke's theories beyond the simple fact that they exist and have adherents that are moved by them. They function poorly as analogy, which is partly why they have so little real-world traction. Dick Cheney is not "like a lizard". Lizards are generally shy and harmless creatures, most of them are helpfully insectivorous, many have detachable tails. The members of the House of Windsor probably rarely eat bugs and Dick Cheney probably does not have a detachable tail. He is like any of us who would allow self-interest and lust for power move us to manipulate others to our ends regardless of their pain and suffering. You can see it at the cash register of your local grocery store if you look for it, you can see it everywhere in various scales, no pun intended. It is a very, very human impulse, to our great misfortune. If you find it satisfying to call that "reptilian", I ask of you: show pity to the reptiles. They are a group of tremendous dignity.
We have very little understanding of the forces that shape the world, really. Power has a price that we, placed under its sway, cannot know of, and perhaps neither can most of those who wield it. We would all like to change the world, but the world changes us, and that is the evil of shapeshifting.
Also...
Interesting thread dynamics here. A newcomer appears on a contentious but respectful discussion and the wagons are circled. I guess there's a minimum post count required before unleashing dickishness upon the membership. We really are an insular family here, it's beautiful. I had thought, though, that there were on the forum any number of folks for whom Icke's work was both revelatory and load-bearing enough to take up swords in earnest. I guess I'm happily mistaken.
But human sacrifice, well, that's another matter entirely. That is, imho, a matter of historical and ongoing fact. We can debate whether Diana fits the bill, but blood is spilt in the name of gaining power. The only question is the degree of overt occultism involved.