It's a seen-and-unseen problem. Wages rising for the same activity is actually rare and historically really weird. The chief way people improve in the world is to automate/creative destruction old professions in favor of more modern ones, and through lower costs due to efficiency. Investment banking enables and accelerates both of those processes.
It's a stretch, but not insane to think that, say, streaming video or iPads might not exist without investment banking.
Someone replies, who cares about iPads or streaming video? But how much have, say, TED talks enabled thinkers to make progress on hard important problems?
The causal chains here are long and complex, it's hard to say for sure. But creative destruction and replacement of old industries with new means better professions, and reducing costs is the other chief way to prosperity. You know about the huge blowups because they're noteworthy, you don't consider what industries wouldn't exist without a gradual re-allocating and efficiency, freeing up more people to do higher level work and driving costs down.
It's hard to do mentally, inevitably someone will reply, "LOL, this guy thinks without investment banking there'd be no iPad!! That's all Jobs and Woz dude!!" I don't know. Maybe. But why is South Korea so much nicer to live in than South Vietnam? Why did South Vietnam start to improve rapidly when they liberalized the banking system and started taking foreign investment? Capital allocation really pulls the world forwards, but many of the gains are subtle and hidden while the failures are prominently on display.