An "independent" Scarborough would be dependent for a lot of things. Transit, police/fire/EMT, libraries, etc. …
In fact, an independent Scarborough would automatically mean the re-establishment of some form of Metro, with the remainder of Toronto holding all the cards over all those files mentioned. An independent Scarborough would be regularly drubbed at such Metro council meetings.
The only way to avoid such a situation would be this Scarborough establishing its own entities (with all the cost and duplication that implies), which would hardly carry much appeal to many small-c conservatives there. Especially as creating a Scarborough Transit Commission would create the very barriers and duplication on transit that Scarborough politicians have railed against.
If an independent Scarborough wants any more subways, it's going to have to pay for them itself. The province or the federal government are assuredly not going to be granting every single wish Scarborough has. Given any Scarborough City Council would quickly run out of fat to cut, user fees or property tax hikes would be inevitable. If city council balked at such things, an independent Scarborough would be in pretty much the same position as it was when in Toronto: wanting all the things, but refusing to consider any meaningful measures to pay for them. Except now they couldn't blame downtown, and different parts of Scarborough would turn on each other.
It's almost as if the people wanting an independent Scarborough haven't thought it through. At all. Could it be?