Regardless of the intricacies of his views, the man does a lot of research. A read through of any one of his books is plenty evidence of this. Much of his research is independently verifiable, and his main focus is helping to show people that they are being taken advantage of. Meanwhile, there are a bunch of people on an internet forum crucifying Icke fans essentially because he believes in something 'too weird.' At least he is spreading a willingness in people to think and question, and not putting down any idea that doesn't conform with his world view.
Mr Icke collated a lot of information over the years, much of which was lifted from contributors to his website. He drew a lot of conclusions, many not based on fact and whilst he is responsible for some original theories anyone can throw a dart in the dark and hit something. When confronted with people who do require tangible evidence rather than hearsay and speculation; a cool reception or to ignore them was the status quo. I have seen him resort to name calling and relying on his following to bully the questioner into submission. I too cannot say with certainty that reptilians don't exist but I have yet to and doubt I will ever see any evidence to support this because logic and reason tells me so.
For my money, whether it's reptilians or insidious corporate conglomerates, secret military weapons and technology; I need hard evidence or at the very least to see it with my own eyes. And even then I may still doubt. It is my prerogative. Just as it is others to agree with whatever he says. To blindly follow anyone though and trust everything they put forward is a very dangerous and silly thing to do in my humble opinion.