As a new person here, I will come out in support of a Scarborough subway but not the current proposal. If I were to support a plan for subway transit in Scarborough, it would be one of the following:
1. An above ground or cut/cover extension of Line 2 to Sheppard East with 4 stops: Danforth-McCowan, Lawrence East, Scarborough Centre and Sheppard East. This is proposed because it can relieve potential overcrowding in between transfers at Kennedy for the EELRT, make transfers accessible (no need to transfer if coming south from SC), and gives McCowan a corridor.
2. A Sheppard extension east (Above ground, at grade or cut and cover, depending on road conditions) to Scarborough Centre. This would increase the number of rapid transit stops in Scarborough while spreading downtown commuters out, and eliminating the need for a Sheppard East LRT. People from the STC will take this Sheppard extension to either Don Mills (to transfer to the future relief line), Sheppard Yonge, or Sheppard West, depending on their final destination. The subway will have fewer stops than the Bloor-Danforth line, so it will, in turn, save commuters time (particularly if they use the DRL to get downtown) as opposed to making extra stops on Line 2. It will also utilize the underutilized Sheppard line and be a worthy competitor with the 401. (Heck, you could even run the subway through the median if you really hated cars).
Reasons for supporting the subway over Light Rail:
1. There are existing corridors with subways running on them: Sheppard and Bloor-Danforth. It makes no sense to force people to transfer (especially people that are already transferring to a hypothetical LRT stop) once more
2. Promotes surface transit terminals. The rest of the TTC's subways run extremely well as a result of there being excellent transfer points between surface transit and rapid transit. This will also include the underground Crosstown. Suburban stations, Light rail or subway, will only be extremely well utilized IF there are adequate surface connections. Grade separated transportation promotes this. You will not see barrier-free bus terminals or even bus terminals at any at-grade in road LRT lines. There's no way to connect them. The majority of Scarborough residents have to take a bus to get to either an LRT station or a subway station, as do all other suburban Torontonians that use the subway. The suburbs aren't walkable, people have to take buses to get to where they want to go efficiently. If people have to take a bus to get to an LRT station, then what's the purpose of all the LRT stops?
3. Fewer stops: this may seem counterintuitive, but when you have fewer stops, you have better transfer points along your rapid transit corridors, and you decrease station dwell time, decreasing commute times. As per my previous point, subways in suburbs only work IF there are surface connections. Even with an LRT network of 30 stops, the only people that really benefit are people that live near the stations. If we look at the existing RT corridor, no one lives around it. No one is going to use an LRT if it has more stops, requires a bus to get there, and requires a transfer at the subway to go anywhere else. This situation might make some sense if Eglinton crosstown trains interline, but we already know that this will not be possible.
4. Plans for the future: The subways may not be utilized the day they are opened. They may not even be fully utilized 20 years after they're opened. But they're not supposed to. They're supposed to be built with future ridership in mind. The LRT meets the expectation for the projected 20 year horizon, not beyond that. What happens then? The case of not planning for the future is what has prevented the city from a DRL and other important transit projects throughout the city.
There's no doubt that the current subway plans are completely outrageous, but the city can do better. If the city and province instead invest money in a Sheppard east subway or McCowan elevated, money allocated for the Sheppard East LRT and Scarborough subway can pay for it, with all other provincial commitments going to an EELRT or even better, a DRL.