It absolutely requires passion. Paying the bills is a little relevant. Everyone's bills are different. The money often isn't that great. Especially when starting out.
You can make a living from it, and more than pay the bills... but you need that passion to succeed and passion for brilliant design in order to succeed. Which, imo, you need to succeed in most things. Talent will only take you so far if you're not willing to push yourself.
When i started in design it was hardly 9 to 5, it was always more like 8.45am to 6.30pm... but i wouldn't work those hours for any other job. So i think passion is a key factor in this profession. Mind you even after 3 years the hours didn't change much but the passion remained.
The only time i seriously contemplated moving agencies was when there was no room to move up or develop as a designer, money wasn't the motivator for change, but passion to do more.
This is an industry that demands new ideas every day, commitment to your work, and always learning. People think it's easy, but we [designers] obviously know better now don't we. If i wanted money i'd work in a call centre, less hours for more pay and considerably less stress.
Anyway, what i'm trying to say is, in my opinion, designers from day one don't think about the money, they think about creating... but, i firmly believe that after a good few years, a mortgage, wife and kids, that passion will turn to apathy and money will play a much bigger role. At that point though, if you're not working to the best of your abilities, do you deserve more money?
I personally don't see how anyone could be a graphic designer without passion at some point! You need plenty of it to get a foot in the door, and even more of it to happily work very much outside of the "9-5" standard most of the time.
And freelancing would require a TON of passion for the activity since you couldn't spend so much energy chasing work without it.
It's not really a job where you can turn up every day and be a drone.