Aahhh, hotels, restaurants, foot traffic, tourists, thousands of jobs... Yeah who needs all of that. I think people are sometimes naive and believe what others merely tell them. The two casinos in Niagara wouldn't be up in arms if it didn't mean that much to that city and it's residents.
Given that Toronto has four new five star hotels about to kick in, new hotels in Southcore, new hotels on Yonge; a ridiculously vibrant restaurant scene, and plenty of tourists, I don't really see how the ancillary benefits are germane to the conversation. The question, really, is whether the casino on its own is good or bad for Toronto.
Atlantic City's beachfront was relatively residential when the casinos took over from the boardwalk as the biggest game in town, and those neighbourhoods are very, very bleak. Slums. The casinos offer zero benefit to a residential neighbourhood, much like the way the Eaton Centre sucked the life off of Yonge for years & years -- they are designed to keep people inside.
However, who cares if the site is already 'inward-facing', like the Ex or OP, as has been pointed out. A permanent casino at the Ex, as opposed to the current arrangement which keeps the place afloat, would make sense IF the CNE/OP got a decent slice of the profits and could use that cash to rehabilitate their infrastructure, I would support a casino there.
BTW -- to the person that said the Ex grounds is dead, you obviously don't go there often. Due to shows in the Direct Energy and Car Barn, games at the Ricoh and BMO, the Queen Liz, Medieval Times, and all the weddings, etc. at Liberty Grand (and throw in Muzik(?), Horse Palace, etc.), the Ex is hopping every Saturday when I take my daughter to ride. Ontario Place is dead outside the summer (and particularly this year, of course), but the CNE grounds are very busy year round. If they can get the cash to do their 'disguise the parking lots' renovation by greenlighting a casino, I'm OK with it. People gamble. The city might as well benefit.