Damn, you're good! I love it.
I'm not a fan of Empire and if you read my writing on monarchy you'll see this shine through. If I could extricate the empire aspect from the enlightenment aspects then I certainly would - but the two remain entwined and the Industrial revolution in particular had a devastating effect on many people in the colonies and in the UK itself. It was a difficult time to be alive but one with a net benefit to future generations across the world.
Your point about the Nazi regime is also well made, the same could be said about Stalin or Mao. I think the effects of something evil like Empire or even Nazi ideology gets mitigated in the fullness of time as the cost benefit analysis becomes more complicated. We hold a far more nuanced view of Genghis Khan for example - his impact on the world was devastating at the time but has come to be understood as balanced and far more thoroughly the further from it we get. Dan Carlin has done a few excellent podcasts which make this point. I wouldn't argue that the Nazi regime was 'good' but I could make the argument that 'some good' came from it.
I would struggle to draw a different conclusion from you when placed in the modern era. I don't think genocide and murder can be proposed as a viable option regardless of the outcome - and yet, we have the Invasion of Iraq by the US and UK to contend with. I'd like to think, at the time the British Empire was unfolding, I would've taken an anti-empire stance and certainly an anti-slavery stance - such things go against my general leaning towards the equity of human life.
Where I would say we disagree is the capacity for imagination, historical analysis and building a more compassionate society come with the stability offered by liberal democracies. People have the psychological space to explore what it means to be kind, considerate and human. Many activists of all kinds who denigrate the status quo in liberal democracies have not considered what the other options are.
I would say colonisation was neither moral, nor humane - but the stasis and pristine Earth you want to see never really existed. The earth is a cruel mistress and lives before science and technology were brutal and short. Whether I would trade the history we have inherited for one where famine may still be a problem, european wars are more frequent and deadly, measles, smallpox and other illnesses aren't researched or vaccinated against - I'm honestly not sure. The suffering may be greater, it may be lesser. We have no way of knowing.
I would say, perhaps predictably, is that there must be lessons learned from where the species went wrong. The antiquated ideas of 'empire' need to be dispensed with (along with the antiquated concept of monarchy) and we need to move to a centre ground understanding of both the good and bad history presents.... binary positions are rarely entirely correct as history and it's consequences are both complicated and nuanced.
You've got a great debating style and you're making me consider the validity of my own arguments - so consider yourself followed and feel free to hold me to account for the things I write in the future. I suspect we will disagree often and I look forward to it. :o)