A good, thoughtful response. I think that we make moral judgements based on intent rather than an unconsciously-produced outcome. But it seems that imperialism seldom intends
harm. It intends influence or wealth, both at the level of the imperialist power and at the level of companies that exploit the opportunity. Beyond that, the effect on local populations is usually an afterthought, and whether what happens to them is good or bad depends on a lot of factors.
Until the early 19th century, with the abolition movement in Europe, it seems that there was very little moral imperative cast upon colonizing powers (ie to be respectful and not exploitative). These days, I think the behaviors of major actors in the world are inescapably scrutinized, and judged against our own moral positions. So whether or not the US currently has imperialist behaviors, the most objectionable acts happen at a different level (i.e. taking advantage of cheap labor and few labor laws in other countries, exploring for oil without regard to environmental impact, buying raw materials on the cheap but selling those raw materials back monopolistically once processed).
On the other hand, there is more of a moral mandate in our treatment of other places. Remember, we're agreeing (I think) that it's the intent and not the outcome that affects our moral judgement, so when we have things like USAID, federal funding for diseases and economic hardships in developing countries, and tax exemptions for charitable organizations, one can argue that our intent
is that our influence and presence be good in the end, and not blindly exploitative.
My feeling, though, is that when people's lives and livelihoods are at stake, it's the results that matter and not the intent. If the results aren't good, the methods need to be revised.