"If that was the case it would be even worse! Not against free speech, but against free thought..."
I'm sorry, what? If someone holds an opinion that opinion is going to be subject to challenges, particularly if it's an opinion that risks being offensive, or is based on factual inaccuracies, misinterpretations, and the like. Protesting against such opinions is hardly an oppression of free thought. What a strange thing to say.
Peter Tatchell's articles suggest that he's long been a champion of defending free speech as far as possible. I don't think that his protesting against Nick Griffin contradicts this -- the views of the BNP were at least borderline racism and probably a great deal beyond that, and had to be challenged and contradicted where they were wrong (which was most of the time) -- particularly as the party started to enjoy some electoral success in a four-year period from 2007 or so. Nowadays the BNP is dead, because in the end it was the publicity they gained that allowed the public to see the party for what it really was.