If you take my city as an example: everything is build around cars, we don't have any bike lanes. To fix this, they painted those dottet lines on the road, easy to ignore for drivers.
The knowledge that they have to take away space from car infrastructure to repurpose it for sidewalks and bikelanes would be a huge step, because there is simply no other solution. Every expertise the city ordered is saying it, but they still won't except the facts and try to weasel out with those painted bike lanes.
So in general you are right, one shouldn't be happy when your gain is based on another beings loss. But in infrastructure planing terms it would simply make the city a better place for everyone.
Exactly. They demolished entire historic, dense neighborhoods and displaced countless hundreds of thousands to build freeways. They took all the streets away from pedestrians and cyclists and streetcars and gave it to cars, save for a tiny sliver of sidewalk. And cars are the most space-inefficient mode of transit, mind you.
All this is doing is reclaiming a little bit of that space back.