Jim,
Maybe you should read the link you posted.
The poster was not posted with agreement of all those who voted for Brexit. In fact your link states:
Johnson, who leads the official Vote Leave campaign, said the poster was "not our campaign" and "not my politics". Drawing a distinction between his own view and those of Farage, he suggested that leaving the EU would be a way of "spiking the guns" of anti-immigrant feeling. "If you take back control, you do a great deal to neutralise anti-immigrant feeling generally," he said, after reporters showed him a picture of the poster. "I am passionately pro-immigration and pro-immigrants."

Immigration is not the problem. Uncontrolled immigration is. Even Angela Merkel now seems to accept that her 'open door' policy for Germany was a mistake.