Today (because we forgot the cost), but not back in the day.
Or because we think it was worth it, in the end.
This. I mean if the people put up with the problems caused by the new construction, I believe they deserve credit for being pro-civilization. Not the "oh no, look their old world is gone" nonsense. Surely nobody rebuilt the city for garnering sympathy.
The old mediaeval city was destroyed to essentially disenfranchise the working poor. No longer would they have strong defensive positions in small winding streets during revolution, they were also displaced from the city centre to make space for the wealthy and elite.
Money and power weren't working towards a pro-civilisation agenda. They were working in their own self interest against the struggling masses.
For example, the state knocks down existing dwellings to build more roads so it is easier for the army to rapidly mobilize and crush unrest.
The state begins to require all subjects to have a last name, where the people themselves have no real need of one, in order to better identify individuals for more effective taxation.
It's worth a read, both for the appreciation of how it plays out in the world, and also as a source of interesting analogies for how other regimes, such as large hierarchical organisations, will embark on grand projects to attempt to make the surrounding environment more legible and tractable to centralised control and governance.
They were always for the purpose. While there are rightful aspects to complain about the displacement sanitation and boulevards were good things even if their motives were ulterior.
Taking for granted that that is nonsense, is the same error, a blind belief that any novelty is better than what it replaces.
There were political motivations behind the change (and impact on the population at the time) not just some noble march towards better.
To give a simple example, bulldozing down Venice to build some Mall-ridden monstrosity that looks like 20000 other places in the world, would not be better in any way, and people would be right to lament about that "old world" being gone.
(Of course many moderns, especially Americans having no history, live in a perpetual now, and can't put things into perspective. They judge all things like mobile phone models, the newer the better).
TBF the people who were affected by them were just shoved out of the city center.