No, asking why things were done in the past is a useful exercise to uncover deficiencies in reasoning, process and other areas which can be acted upon for present and future action.

Your argument is essentially "don't ask why my favored party/people/orgs did bad things, just pay attention to the rhetoric they're using now." It's an incredibly cynical position to take, in my opinion.

It's cyclical to be constantly looking back and holding every group to this impossible standard we've constructed for today that is constantly changing. This is the only argument I ever see from Trump supporters: Clinton or Obama or the Democrats did it/would have done it or worse, so it's all okay and you aren't allowed to complain. Never is the argument presented that what is currently being done is right, because it's indefensible.

Why not talk about what is right and talk about doing that? When we read 'all men are created equal' we don't say 'well, the founding fathers hated women so it's okay for me to' or 'the founding fathers had no good ideas and they are trash' we talk about what parts of their ideas had merit and try to improve upon them and do the right thing /today/, from this moment forward.

What makes you think I support Trump? My criticism comes from the left, not the right. The difference between Hillary and Trump has always been one of style and in some areas depth, not substance. Suddenly Hillary's supporters decide to protest and support anti-Trump action, when the entire Democratic establishment supported the very things that have set Trump up for years without a peep. I'm deeply skeptical and do not trust them. Period.

Seems pretty easy to resolve this dispute: let's both act in the present and critically consider our past actions. Where's the argument here?

No argument on that specifically. I do take note, and exception, when very vocal supporters of Hillary have a "come to Jesus" moment over Trump's actions. Part of that "critically consider past actions" thing.