Alan, full text of the speech here http://www.telegraph.co.uk/comment/3643 ... peech.html
He did not advocate violence and I can honestly believe he was trying to warn and avoid what he saw as likely violence. He was, however, against continued immigration and argued against anti-discrimination legislation. From a present day perspective, many would class that as intolerant (though it's a word which is used rather vaguely without precise definition). In the context of 1960s immigration policy and Powell's liberal views it's a lot more arguable. I'd say he was motivated by conservative desires to prevent demographic change and liberal beliefs in the rule of law rather than a prejudice against immigrants.
Part of what he got blamed for was the reaction he provoked. In a way this is the problem we see whenever anybody makes any attempt to discuss the negatives of immigration. Inevitably some racists support the person/party and they then discredit him/it by association. The phrase "Enoch was right" became the catchphrase of supporters of the National Front in the 70s which made it impossible for sensible people to appear to agree. It killed most parliamentary debate on the subject for decades.
People also criticised the emotive language of the speech. A classics scholar like Powell may have understood the reference but talk of "funeral pyres" and "the River Tiber foaming with much blood" appeared to many others as being all a bit apocalyptic and a potential spark for racial violence.
Bringing this back on topic. I think the decline of liberalism is reflected in the cycle helmet debate. It almost always revolves around the efficacy of helmets and the effects of helmet promotion and laws rather than the sanctity of individual liberty. Even many of those who wish for it to remain a matter of choice wish it out of practical concerns such as uncertainty about efficacy and concerns about cycling levels rather than a fundamental belief in freedom. Sadly, the modern belief in parliament's inalienable right to interfere in people's self-regarding actions is one on which both red and blue parties agree. We'll miss them lib dems.