It’s not really excusing anything, just pointing out that Cantor Fitzgerald would be making money whether this Supreme Court ruling went for or against the Trump tariffs. So it’s not like they had to have any inside knowledge to be making money.
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.
It stretches your imagination to conceive of a financier chasing short term gains over the long term stability of the investment bank they are part of? I seem to recall an event back in the late '00s that you may want to look into.
Ah yes, instead of applying the normal legal standard of “not even having the appearance of impropriety” we instead apply the monkey’s paw standard of waiting until they “no longer even have the appearance of propriety”.