Again, the argument was that something was built. Nothing particularly useful for the majority of people at the time being, but something. It's better than the money being spent in other cities (if I remember correctly, there was a lot of provincial funding), or the money going to freeways, which it likely would have.
Side note, if the city ends up opting for LRT, the city will have to foot the bill; the federal and provincial governments will likely not pay a dime if we revert to LRT (this is because the provincial government needs the corridor to upgrade the Stouffville corridor to RER, and this can't happen with an LRT running down the corridor without massive expropriations (which will probably cost more than tunnelling for the SSE). The LRT will likely cost at least 1.4 billion as is, but if costs rise (like with the subway, they likely will), the city will have to foot the entirety of that bill. 1.4 billion + inflation + capital cost increase. I estimate that it will cost around 2 billion dollars if it's actually built (for viaduct rehabilitation, rebuilding tracks, rebuilding of power and signal systems, rebuilding of all 7 stations, the extension of the line etc). Think about that for a second, the city is currently footing $800,000,000 of the $3.56 billion. It's much less than the 1.4-2 billion dollars required for the Scarborough LRT. Unfortunately, this is a no-win situation for everyone. The city is trying to make the best out of a bad situation by building the subway to the STC (where a lot of the buses in Scarborough terminate), building the EELRT to densify Eglinton and to promote mobility through scarborough, and by adding additional RER stops in scarborough to promote development and quicker travel to downtown (Note: taking the subway to yonge and Bloor or Yonge and queen would be faster than going to an RER station, heading into Union, walking the even longer transfer to the subway at union, then taking the subway to the downtown workplace. It's only useful to scarberians if you're travelling to Union, or anything south of King).