Controlled immigration where the immigrants integrate is very good for any country, uncontrolled immigration especially where integration does not take place is a disaster.
Mr Blair and his cohorts introduced uncontrolled immigration and on top of that actively encouraged immigrants not to integrate (The great failed multicultural experiment). Cameron has failed to stem the flow, partially because of the Lib Dems, partially because he is weak on Europe and partially through arrogance of what the public want and perceive.
The problem with uncontrolled immigration is that the infrastructure cannot cope; schools, Roads, Hospitals, Police, housing the list goes on and thats before you get on to importing criminals and paying out benefits to people that have not paid a penny and want to murder you.
So no Mr Cameron, immigration over the past 15 years has not been good for Britain.