Accusing Nick Griffin of being stupid undermines the threat that he poses. There is no shortage of stupid politicians, but Nick Griffin isn't one of them. You are just bandying about the term "stupid" as a sort of insult. It is an innappropriate insult for this particular person.
Know your enemy. Never, ever, underestimate your enemy. You may despise his racism, but the man is neither ignorant nor unintelligent.