Air Canada My legitimate ticket was a fraudulent promise of a seat Internet

I purchased a regular price return ticket (Calgary to Vancouver) on Air Canada a month in advance of a business meeting that was on a tight schedule. 

At the time of booking I declined the "optional seat selection" for $40. It's a 1 hour flight - so I didn't really care where I sat. 

When I got to the airport to check-in (2 hours early) they wouldn't give me a boarding pass. Instead they gave me a "standby" pass and marked my luggage with a "standby passenger" tag. YES I protested. I didn't pay for standby and I wasn't a standby passenger. 

The helpful ladies at the luggage check informed me that I would have to sort it out at the desk at the gate. For this - I needed to be at the gate early so they could assign a seat or straighten it out. 

I showed up early - no one was there. After waiting anxiously until boarding time to speak to someone, I was informed that I had been downgraded automatically because I hadn't purchased the optional seat selection and they oversold the flight. So there was no seat for me on the plane unless someone volunteered to give their seat up. 

I did explain that I had an important business meeting and that I selected Air Canada specifically because of the time of the flight and for no other reason. My first meeting was with people flying in from overseas. We left a small margin of time in consideration for flight delays - but I was expected and had arranged for transportation already on the other side. 

I was given the crazy explanation that "all Star Alliance partners" overbooked their flights because of no shows and only those who paid extra for the optional seat selection would be guaranteed a seat because the airline wouldn't bump off passengers who paid more. 

In the end I was given a seat - but the flight was delayed by over 30 minutes to give them time to find enough people to give their seats up. If they hadn't found sufficient people - me and my ticket would remain on standby until a seat became available on some other flight later in the day. ...cause that's apparently how standby works. 

Air Canada - I don't really care. If you oversell your flights that's YOUR problem - not mine. Figure it out. Downgrading a paying passenger is not acceptable - ever - anywhere. 

There are other airlines flying those same routes and they have never treated me the way you did. It's shameful. Doesn't matter that I got a seat in the end - you had no right to sell me a ticket that you didn't intend to honor. If you oversell - make the oversales purchase standby.