Congrats, worst article I've read on Medium.
1) The infrastructure in those places was not sustainable in many cases, used forced/slave labor, kicked out the native residents, or destroyed the environment.
2) Hilarious, because this goes AGAINST your point! That means it was bad for the colonizers too! I'm also betting you're the type of person telling black folks to "get over" slavery, but here you are whinging that your grandparents paid taxes.
3) You do realize these places were colonized...and the slaves came from that...right? "Ending slavery" = "ending the very thing colonialism enabled and encouraged." And actually, that 1848 date is when France RE-abolished slavery, post Revolution France abolished it in 1794 and Napoleon reinstated it. A simple Google search of your own nation's history would have saved you the embarrassment, but like all right-wingers, you're too lazy to actually do the bare minimum research.
But besides those erroneous and misleading dates and poorly-cited sources, this reads so badly that I feel like I endured a copy/pasted school report where you were asked to play devil's advocate in what is clearly not your first language, but the saddest part is that you believe this because you are willfully ignorant. In other words, it sounds like you don't know Jacques-shit.