Recommend watching the Netflick 2016 documentary, “The Jihadis Next Door” to see how well that “opposition to racism” is working out for Britain.
Its open borders with European countries is problematic, at the least.
The United Kingdom does NOT have open borders with the rest of Europe. It's never been part of the Schengen open-border area, in which not all EU countries participate. Consequently when the UK refused to join in the EU's Merkel-inspired plan to distribute Syrian refugees on a quota basis throughout Europe, the EU could do nothing to enforce it. Consequently also the notorious (now closed) 'jungle' camp at Calais, where migrants who had made it across the rest of Europe became stuck at the UK border.
The only immigrants which Britain was obliged to accept under its EU membership were people who were already citizens of other EU countries, exercising their right to live and work in any other EU country. Third-world immigration to the UK was affected little, if at all, by EU membership. It's been the responsibility of successive British governments, not of the EU.