I don't think it's hyperbole. In other cases where FTT was introduced trading volume dropped 93% (Sweden). So that's pretty much every US based broker, exchange, clearing house having major major profits issues.
Then add in secondary effects of the loss in capital gains taxes from the trading and brokerage industry.
But most importantly the inability for commodity companies, mortgage companies, anyone doing international trade to hedge effectively and the knock on effects that has. I know traders that work for Cargill and Glencore that said they couldn't properly hedge anymore if this tax came in.
Of course this is based on previous examples of where FTT has been introduced (and almost immediately reversed) and US case may not play out exactly the same.
But it's serious stuff