funny "birdy I have no idea why you are justifying yourself." - I don't think she's 'justifying herself', I think she's explaining, which is fine.
birdy "I can say with 100 percent clarity that we did our best and it's all worked out in the end." Then hold on to that knowledge and don't feel bad about what anyone else is saying. 
For me it is the nature of dogs that makes rehoming such a sad option; they are a family group animal who tend to bond very strongly with their owner, and suffer confusion and distress when parted from that owner. Obviously it varies from dog to dog how devoted to their owners they are, but for some dogs it would be very traumatic to be parted from their family and kept in a rescue kennel. Cats, on the other hand, tend to be attached to places as much as to people (another generalisation, I know) - hence cats going miles back to their old house after a move, or buggering off to a new home at the drop of a titbit.
OP I think most people do things in their early 20s without a lot of forethought - I had two very large snakes for a number of years which I eventually rehomed, and I've also rehomed guinea pigs and rabbits when my circumstances changed (so now you can splutter 'pot... kettle... black' at me if you like
). But these were animals that were bonded to each other, not to me (and the snakes weren't bonded to anyone), whereas my dog is devastated if I go to the loo without her, let alone think about rehoming her.
Look, you did the best you could, and it worked out fine, so don't let anyone upset you. As someone else said, if this thread makes someone think a bit more about whether it's sensible and responsible to get a dog (or breed of dog), then it's a good thing.
And seeker of course noone knows where they'll be in 15 yrs time, but you can make educated guesses, look at your plans and priorities (travel, kids, career etc) and attempt to make a responsible decision.