Actually the Dark Side of Trickle Down = Deficits (and the interest on them). Extra and excess debt.
Then there's a choice. Raise taxes when the tax cuts fail to pay for themselves as promised. Or cut spending.
And btw, there are numerous billion dollar companies paying zero corporate tax.
Then when the plutocrats opt for the latter, there's still a choice of what spending to cut. Defense and corporate welfare could be reduced. Also agriculture spending/welfare. It doesn't have to be services for the needy (mostly elderly, women with children, and the sick).
It's all a matter of choices and priorities, which often is played like a rigged shell game.
Really the dark side (ie hidden evils) is the increasing inequality which has a pernicious effect on society and politics.