The Viaducts act as a fifth bridge onto the downtown peninsula. And not all the vehicles using them are local people too lazy to commute on public transport. There are delivery vehicles, emergency vehicles, and out-of-province vehicles accessing the city centre.
Otherwise stated, the viaducts (and they're not humungous eight-lane thingies, at that) are a vital link eastward from downtown - although I admit something should be done from where they rejoin the streets east, so as to impact less on Strathcona and immediate neighbourhoods.
The Bottom Line: just how much usable free land do they cover up now? Is it really all that necessary and all that profitable to tear them down, creating a slower, more awkward traffic scene (and the vehicles will
STILL be there ....) with red light, stop, go, stop, go, left turn, right turn, traffic-backed-up situation?

.....
Taking out the viaducts, IMO, is a "granola-muncher" idea. Excuse me. PLEASE ... keep the viaducts.