Can someone explain why tallness subtracts from a neighbourhood? Even if it were proposed for the centre of a low-rise neighbourhood, why is a tall building like this objectionable?
Interesting question.
One impact is visual - but real. Shadow impacts can affect gardens and parks. Tall towers can also take away privacy: tower units can peer into back-yards and windows. Visually, from street level, where there was once sky, there will now be a large object, looming like a monolith. This might not be a big deal in the downtown core, where there are plenty of buildings all around. But outside the core - even a few blocks over, in areas like College or U of T - a gigantic tower alone in the sky would become visually imposing, dominating the scene - it can be an incredible distraction. What's more, it changes the character of the neighbourhood. If residents valued their area because trees, brick and sky prevailed, the arrival of glass and concrete is a jarring transition.
(Already, I can hear people saying "It's a city, get used to it!" But remember that cities combine all kinds of different neighbourhoods, with all kinds of different feels. And yes, cities change and evolve. But it's best if that happens gradually, not violently. Imagine what walking through Kensington would feel like if they'd built First Canadian Place across the road, on the north side of College, looming over the whole affair.)
Then there are the more practical effects. Big buildings house lots of people. They create foot traffic, vehicular traffic, transit traffic. This is fine and dandy where the city is built to support it. (Like Yonge and Bloor.) But when you built big buildings in suburban areas, you end up with a situation like Sheppard, where subway-driven mega-developments butt up against ranch-style housing cul-de-sacs, and headaches ensue. Since there's little mixed-use development in the area, you end up with huge influxes and outfluxes of people at peak times, and infrastructure that's underused at other hours.
In today's condo market, tall towers are built with tiny units that can't house families; the result is a lot of investment units and transient tenants. So they're unlikely to integrate fully with the local community.
And finally, there's the fact that development begets development. There's no such thing as just one tall tower: It becomes a precedent that developers can use both with the city and at the OMB. This has an effect on land values. Up on Sheppard, these towers were very literally going up in homeowners' backyards, leading to trench warfare between community groups and developers a few years back.
None of this is a screed against tall towers; I like 'em too. (Though I'm really concerned with the types of units we're building in them.) But this is why planners have learned to avoid putting tall towers in non-tall neighbourhoods: They can drastically alter the quality of a neighbourhood visually, economically, and practically.
