The poster is racist because it very clearly echoes Nazi propaganda. How can anyone possibly defend it?
Ok, this is a highly emotive poster - the image and the large text reading 'Breaking Point' dominate it. The emotions it seems to evoke, from the framing which suggests a never ending stream of people to the prominent text, are those of fear and intolerance. It presents a group of people, who are dispossessed and seeking help, as a threat. In order to suppress our sympathy for their (undeniably awful) plight, it has to dehumanise and 'other' them - that's how racism works. You have to present the people as a homogeneous mass, different to your target audience and dangerous towards them - in this case,it's the phrase 'Breaking Point' which hyperbolically conveys an immediate and extreme crisis, which of course evokes panic and worry. It is not designed to stimulate reasoned discussion. It is not attempting to present facts for calm and considered debate. It is fearmongering. It promotes division. It incites hostility. It is not Farage bringing the question of immigration, listening to counter arguments against his own viewpoint and coming up with solutions. It deploys well-used racist techniques to produce an emotional response.