Maria, before we even get to the bit someone else posted, look at the bit you posted:
" Here is a decent, ordinary fellow Englishman, who in broad daylight in my own town says to me, his Member of Parliament, that the country will not be worth living in for his children. I simply do not have the right to shrug my shoulders and think about something else. What he is saying, thousands and hundreds of thousands are saying and thinking – not throughout Great Britain, perhaps, but in the areas that are already undergoing the total transformation to which there is no parallel in a thousand years of English history. We must be mad, literally mad, as a nation to be permitting the annual inflow of some 50,000 dependents, who are for the most part the material of the future growth of the immigrant descended population. It is like watching a nation busily engaged in heaping up its own funeral pyre. So insane are we that we actually permit unmarried persons to immigrate for the purpose of founding a family with spouses and fiancées whom they have never seen.[4][5]"
what Powell is saying here, is that England will not be fit to live in when there are too many people who have come from other countries; and that it is mad to think we can live alongside them.
this is racist because it implies that there is something innately particularly awful about the people who are coming that make them unfit to live alongside. this is wrong.
(and it is abdicating England's responsibility to the world as a formerly colonial nation. England did not sit about minding her own business to look up one day to find that people seemed to want to come here; England barged about the world, taking what it liked, grew rich on it, and now has to face up to what it means to belong to the world)
and the "foaming with blood" is either implying that the "other" will be shedding "our" blood, or inciting "us" to shed "theirs", or both