The party leader said Ukip's opponents were "screaming blue murder" over the images because they did not want to have an "honest conversation" about immigration.
His robust defence came after religious figures joined MPs in condemning the posters, which have been funded with £1.5 million from businessman Paul Sykes, a former Tory donor.
One poster says 26 million people in Europe are looking for work, adding, with a picture of a finger pointing at the reader, "and whose job are they after?".
Cardinal Vincent Nichols, leader of the Catholic Church in England and Wales, said it was wrong to use expressions that suggested "dismay or distress at all these people coming to this country".
Tory backbencher Nicholas Soames described the poster campaign as "deeply divisive, offensive and ignorant", while Labour's Mike Gapes branded the posters "racist".
Jim Murphy, the Shadow International Development Secretary, said Ukip's euro election launch was "another desperate cry for attention" and suggested the party's online support was not necessarily all it appeared to be.
"It happens here in Scotland, where you have a thing called cybernats, who take to Twitter to insult anyone who wants to keep Scotland part of the United Kingdom, and to some degree Ukip have a similar group of people who are just so obsessive, so determined and so focused, they spend a lot of time on their phones or computers insulting and making accusations for no reason other than they disagree with them," he said.
But Mr Farage, launching his party's campaign in Sheffield, said: "The fact Westminster hate it and want to scream blue murder over it is because they have opened up the doors, they have fundamentally changed the lives of millions of people and they would rather we did not talk about it and just brush it under the carpet."
Mr Farage was also forced to fend off charges of hypocrisy after it emerged he employed his German wife, Kirsten, as his office secretary.
The MEP denied she was taking a British person's job "because I don't think anybody else would want to be in my house at midnight, going through emails, getting me briefed for the next day. Nobody else could do that job. I don't know anybody who would work those kinds of hours."