Nobody is against more capacity, the question is if it is necessary, and unfortunately the numbers we are throwing around to decide if this is the case has mostly been conjecture. We're throwing around numbers like "30% less capacity" with very little evidence that this is the case. We do not even know what vehicles the Ontario Line will be running yet we are forming assumptions after assumptions, and the people on here who desperately want to prove that the Ontario Line won't be enough are stretching numbers to be as "worst case scenerio" as possible, and are justifying this by making Metrolinx and Doug Ford look as incompetent as possible, that none of the engineers working on the Ontario Line are aware about how they're making something that won't have enough capacity, and that the only people who know what the city actually needs to fix its problems are the members pushing for the DRL.
We could make the Ontario Line have a ton of capacity. We can expand the tunnels and run GO EMUs under Toronto so that capacity never becomes an issue for the rest of time, however that costs a ton of money. Even if we take the worst case scenerio if the Ontario Line has 15-30% less capacity than the DRL, if building shallower stations and opening ourselves to less tunneling means that we get less capacity for half of the cost, that's an absolute win. Let's do some math. Let's say we have a budget of about 20 Billion dollars. Option 1 we build a single subway line at a peak capacity of 36k ppdph, and option 2 is for the same price we build 2 subway lines at 25k ppdph (30% less capacity). The 2nd option offers the city significantly more coverage, offering subway service to more parts of the city, and introduced an additional 50k ppdph into the city, for the same price as a single subway line that only introduced capacity for 36k ppdph and did not extend the coverage of the subway system as far.
With the Ontario Line this is what we're effectively doing, except the capacity isn't 30% less, its maybe 10-15% less.