Thank you all for all these answers.
I need to study this issue more closely before I can establish a solid opinion on that subject.
I'll keep this thread open, and any additional comments are highly welcomed.
When I feel I have a full understanding of that problem, I'll respond to everything...
Why are particles in QFT assumed to be point-like?
This assumption is the source of ultraviolet divergences.
Does anyone know what is the source of this assumption, and what happens if you assume that particles are not point-like?