The left are obsessed by immigration because they cannot have society coalesce around any totem except the state. It is important to realise some of the base assumptions of the Left; 1. The only value of a person is as an economic input; 2. The highest attainment of the individual is intellect. 3. Economy is Science and science is unbiased and fair. (this view is rooted in pernicious proto-fascist doctrines advanced at the beginning of the 20th century by the likes of the Fabians and Eugenicists) It follows then that Human Beings have no intrinsic value. In fact they are wholly expendable in pursuit of the great projects of State. (Utilitarianism) Thus people or communities are not seen as useful or relevant. In fact, they see any organisation beyond their control as offensive. (as was recently displayed in the Brexit ref, they cannot conceive that their economic model might be wrong; All opposing forces are Racist or anti-Muslim or somesuch). All must be reliant on the state, as the state is the arbiter of all that is good and just. If you only value things in terms of their economic utility, then Religion, Race, Community, Family must all be swept aside in the name of Economy. All are equal and every thug, deviant and fuckwit has an equal value. There can be no exception. The model State, and its assumptions, dictate this. In times of trouble, Immigration dilutes and weakens parts the of society most likely to militate against this dogma. And so we have seen this occur. It is no coincidence that just as modern Economics - thought, theory and practice - has been pulled asunder by the great crash, that the Left have begun to implode. This is not confined to Britain, nor is it over. Not by a long way. tl;dr - the intellectual basis of the Left has been proven to be false, thus the totems crumble, leaving the people at the mercy of market forces; which they are now militating against.