I find GO Transit to be very efficient
Clearly, you did not ride the same ones I rode. They were underfunded, most lines operated only during rush hours (gosh, why don't we try THAT with the subways and see how it affects ridership?), and broke down at least twice a month when I depended on them. That's why I stopped depending on them.
Just because there is a certain population number, it does not mean that it justifies subway construction. Subways demand people, yes, but a particular urban form and density that simply DOES NOT EXIST, nor will it exist for a long while, in the 905.
This is an argument for not having public transit,
at all. The corollary position is the reason we build transit hubs, and Mississauga has several. The same ones that serve to gather people (who'd otherwise be driving) to buses and, yes, even GO trains would do just as nicely coalescing riders for subways. The same as they do in suburban areas of what was Metro, and have from the 50s on up.
This is why you don't see New York City building more subway lines into the suburbs. This is why you don't see London building more tube lines into the suburbs.
They DO build them out to the suburbs; they HAVE built them out to the suburbs; in many cases, the stations that are now heavily urban were built in areas of low density decades ago. This served two purposes: it made the construction less expensive and disruptive than it would have been once the area was heavily built up, and the presence of decent public transit itself served as an impetus for people to move in higher numbers to those areas, creating the high density. If we don't believe that building transportation facilities will serve this purpose, why are we bothering? People are already spread out, and they already have cars. Arguments I'm seeing here suggest to me that's pretty much how it's going to stay. Of course, over the past twenty years, that's no surprise. I've seen them link the 403 and 410, extend the 404 and 427, and built the entirely new 407. Haven't seen them build a single subway station even to the border of Toronto yet. Colour me shocked that this attitude persists.
If money were not the issue, I would love to see subway lines built everywhere in the GTA. Trust me, I would. But you have to be realistic and use resources that are being shared by everyone wisely.
Well, we found the money for all those highways; we found the will to build them... I guess it's because we weren't counting on the goodwill, understanding, or compassion of people downtown.