Look, I'm not against pop-ups if they're done well. Being able to add more livable space to a house built 90-100 years ago in a city that doesn't have much in the way of expandable space is a great idea.
My neighbors "popped up" their attic into a full, usable floor that you don't notice from the street and can only see from the rear, and even then it looks great and fits into the design.
Even the conversions where a developer (or owner) converts a house into a two or three unit condo can be acceptable (within reason, and that can be argued). If done well, as in this example in my opinion, I think the building can fit in with the existing visual design of the street (not talking about parking or other issues here):
But THESE pop-ups on Kennedy Street... damn. This is why we can't have nice things.