Are you against the idea of European cooperation in general? Or against the implementation?
If there is to be European cooperation that goes beyond heads of states talking to each other, you're going to need some kind of space where they can do that. Using that building as a symbol seems like an obvious choice albeit not a very creative one. Really struggle to see how that choice can be "extremely insulting".
I'm against ugly soulless buildings. Those buildings can't be a symbol for anything, because they, like all modern [1] buildings, were deliberately designed to remove all identity. They are completely generic, no different from modern buildings in Beijing, New York, or Dubai. The only thing they represent is a capitulation, or refusal, of making things beautiful.
I'd vastly prefer some national landmark of the nation that committed war crimes against us in WWI & II, than that.
[1] Or is it "modernist"? Whatever the "style" of basic geometric shapes in steel and glass is called.
A movie showing an external shot of the White House establishes that we're going to be looking at the US President next. A movie showing an external shot of the European Parliament establishes... office drones working in the Business Factory?
I don't think the ECB will ever be recognizable (or at least won't become recognized via exposure), since it's just a glass tower like thousands of others.