I do not think that a lifting belt is required. They can be of some benefit, but not a requirement in my eyes.
Anti belt arguement:
Lifting without a belt will help to build the core muscles and make your body stronger as a whole unit.
Pro belt arguement:
A belt can actually make you stronger as it enables you to push your abs against it and create more stability.
My personal opinion:
I only use a belt on my top work sets. I make sure that I am working my core with the lighter sets. Adding the belt for the top sets ensures that I am applying maximal effort to the lift.