It is not uncommon for an airline to hold a passenger at the point of origin if they know the entire series of flights can not be completed as booked.
By doing so, for many passengers it means they simply go home and return the next day. For non-local passengers it means some lodging and meals to be provided. For legal responsibility it is simply a cancelled flight, rebook or refund (and yes there is probably some PC EU rule requiring a certain amount of compensation).
By sending passengers part way, it means accommodation and meals for all. It means more anguish and complaints from passengers about the uncertainity of reaching their destination and sitting around in the midpoint airport hoping to get on some flight. For legal responsibility it means an interrupted flight which carries more rules, regulations and potential for compensation.
While the OP preferred to fly, the airline has to set a single policy for the issue and holding passengers at the origin is the one most airlines enforce. I have been caught in the same scenario flying Florida to Thailand and was held at the point of origin in the USA, so it is not exclusive to Qatar.
Can you complain, of course you can, but ultimately if the airline followed through on their responsibilities for a cancelled flight there won't be any compensation, other than maybe a small token of apology (frequent flyer miles, etc).