Having done an internship at a major airline when I was in college, I can tell you that it was one of the most rewarding experiences that I ever had. The insight it provides, opportunities it affords, and connections that are made, both with your supervisors and with fellow interns, cannot be replaced. One of the best pieces of advice that a retired captain at the company I worked for gave me was to "enjoy the ride" and I could not agree more. You have, potentially, 40 years to fly airplanes but only one chance to go through college, and you definitely don't want to have regrets about what "I should have done."
The argument about the need to build hours is a valid one because let's face it, you typically will not be able to get hired by a company unless you meet their minimums. However, keep in mind that the industry we are in is a highly competitive one, with plenty of pilots that have the same ratings, same hours, flying the same type of airplane as you. What is going to set you apart from the rest? What is going to give you the edge over everyone else? This isn't to say that not taking an internship will close every door in this field. It may, though, open some that otherwise would have been shut.
As far as setting you back is concerned, it is definitely something to think about because, as it is a cyclical industry, the risk you take is that the airline that was hiring 6 months ago at the hours you had may no longer be hiring once you get done with the internship. For better or for worse, I have always been one to take my time in this field and, although I was set back a few months, I eventually graduated, finished my ratings, instructed to make 135 minimums, and am now freight doggin' it (and having a blast!). Ultimately, it boils down to your priorities and what you want out of this profession, something only you can answer.
Whatever decision you make, always remember to hold yourself to high standards and learn as much as you can at whatever stage of your career you are in. It is going to make you that much better of a pilot. Good luck and fly safe!