Comment by importantstuff

No one who has replied to your question has got the right answer. https://physics.stackexchange.com/questions/21753/why-do-ele... has the right answer. There are multiple aspects to this argument, but essentially, the symmetries of your system force the charges in the Standard Model (quarks and leptons) to be the way they are due to gauge anomaly cancellation. If you believe in quark confinement, which is extremely well motivated, computationally, theoretically and experimentally, then the fact that the proton has exactly charge +1 follows naturally.