Bourgeois liberals' self-flagellation about the British empire is not genuine guilt. It's arrogance masquerading as humility. It's a performance that gives them a high status in their political circles while allowing them to demonise and blame the post-industrial working classes

...the descendants of the people who had least to do with that history, but who don't have humanities degrees so don't understand the right postcolonial critical theory buzzwords which would allow them entry into these circles.

The fact that they gloss over, downplay or flat out ignore the similar histories of other European countries shows that they don't genuinely understand or care what imperialism is, or what the problem with it is.

"Imperialism" doesn't mean flag waving. It doesn't mean attitude. It's not a synonym for blind patriotism. It means exercising power and control over other countries, by whichever means.

So if your pro-EU stance is "it's arrogant for Britain to think we can exercise global influence alone, we need to more humbly exercise global influence as part of a bloc with the other former European empires" then this is not actually as humble or anti-imperialist as you think.