It's true that a volatile environment in general is good for certain types of investment banking business, including facilitating this trade. I nevertheless think it's unlikely - honestly, a galaxy brain take - that Cantor Fitzgerald or other investment banks with influence in the Trump administration would push for policies like unconstitutional tariffs just to drive trading revenue. Maybe the strongest reason is that other, frankly more lucrative investment banking activities, like fundraising and M&A, benefit from a growing economy and a stable economic and regulatory environment.