I think at University it's becoming all the more necessary to take summer jobs. The experience is very important when it comes to competing for you grad job, which I assume you will actually want. It does give you a big advantage if you have already had past work experience, in anything!
My course is pretty full on too, and as much as I would like to chill out and unwind, I need to get on with it and get some work experience. I actually took my first summer off, but when I got back I saw that my friends had summer jobs left right and centre. Luckily I'm on a 4 year course, so I could afford not working in the first summer.
I don't think you're being ungrateful, but I think that at Uni when you are hoping for a job at the end, it's not school anymore and you can't just spend the whole 3months chilling.
ps. That said, doing a job you don't want to do isn't the most fun thing in the world! So if you really don't want to do it then don't take it.