A new television commercial in Toronto calls on voters to "vote for candidates who will keep the [Toronto Transit Commission] public."
If I were one of the experts quoted I'd be a little insulted by it, though we understand that this is the nature of TV commercials.
There are many different ways to involve private enterprise in funding providing transit services, and these are so different that vague talk of "privatization" simply doesn't illuminate what's going on.
At one extreme, you can privatise operations, planning, fleet, public information, branding and almost everything else. In this model, prominent in Britain (but not London) and in British-influenced countries like Australia and New Zealand, government merely subsidises services that wouldn't make a profit, but doesn't try to control the overall planning of the network. This approach sometimes "works," in a political sense, in areas where you have low expectations for transit overall, such as rural areas. It's been very problematic in urban areas, because it deprives government of the control that its subsidies should be buying, and makes it impossible to plan rational networks that would meet the shared goal of a city and its people, and that would use limited street space efficiently. Sydney, Brisbane, and Auckland all went far down this path and are trying, at various speeds, to pull back from it and re-assert government control over most aspects of planning and marketing.
At the other extreme, you can privatise operations only. This is the model used in a number of lean North American operators such as Southern California's Foothill Transit. In Australia, only Perth takes this approach, but it's very successful there. A public agency answerable to voters keeps full control of planning, and also owns the fleet and facilities. Private operating companies are hired only to provide operations and maintenance, under contracts to the agency that are periodically re-opened to competitive procurement. This is a targeted kind of privatisation aimed at the functions that are the biggest budget-killers for all-public agencies: labor costs, labor relations, and liability related to operations and maintenance. You can make a good case that the private sector is in a better position to handle all of these than government agencies are, and while I won't argue the whole case here, many agencies -- especially newer agencies that don't have legacy labor commitments -- are finding this a very good model. In Australia, Perth works this way, and other cities are moving this direction.
You can find examples anywhere on the spectrum between these extremes. Finally, briefly, there's a whole third kind of privatisation that's about the development of major infrastructure, typically called a public-private partnership. This seems to be what Yonah Freemark is referring to in the ad's scare-quote about Vancouver. While the PPP that built the recent Canada Line has been deservedly controversial, Vancouver's operations aren't privatized at all; they're run mostly by subsidiary companies owned by the transit agency, Translink, and that agency is very much in control of presenting a single unified system to the public.