I suppose I can weigh in here, but I don't want to slap anyone's hand or get my own slapped in return. No lies here - I have given my tickets away when I couldn't get any loved ones to commit to the date, but I gave them away on the tram or at the gate, and I accompanied the happy families through the ticket gate as per the terms of the season pass.
As for this morality debate, it's been a rich one. I'm glad there are still people out there who even care about morality in the first place. First of all, if it's wrong for you, then it's immoral for you. Period. That shouldn't be under question at all. Secondly, if SDC wants to turn its head to allow a freebie to sneak through, then that's their business, but it really doesn't answer the question of whether it is immoral for the pass holder or the free ticket bearer. A clerk could also turn their head to allow me to rob the store when the manager isn't looking - it's still wrong to rob the store. And if the manager approves, it's still theft.
I know the argument - that SDC isn't going to profit over a ticket not used - people spend money once in the park - but by not holding myself by a written agreement (terms, conditions), I have broken a written "contract". I suppose that makes me a little bit dishonest, whether SDC still profits or not. The ends rarely justify the means. I doubt if very many people really have SDC's welfare in mind when they use free tickets in this way.
Then there is the issue of scalping the free tickets - myself profiting from the service of someone else - that just doesn't seem right at all. The service being sold still belongs to SDC until it is delivered. I can't really see how I could sell something that doesn't belong to me. The item being sold is not the ticket that I possess, but the future service the ticket affords me.
Finally, I'll bring in the idea that if more people paid SDC and not individuals willing to part with free tickets, maybe (though I'm not naive enough to believe it would happen) season pass and admission prices could be reduced. I'm paying for those free tickets, a point appropriately raised by KBCraig, and someone else is paying a reduced price to someone else. Even if that's not immoral, it doesn't seem fair (but life's not fair, right?).
This is a good debate to be having, and it does us all good to weigh the issue. To each his or her own, but even if I don't always succeed (with Biblical principles in mind), I will always try to correctly make decisions for myself.