Blues with inadequate skills must compete against reds who are restricted to melee weapons, limited to some projectile weapons, as others have stated.
It's not fun to rebel as a low-health class, or when the entire blue team is stacked with snipers that are just beyond broken on certain maps that are just flat open. Blues shouldn't have crits since they have advantages with long-range weapons. In terms of crits, the balance can vary based on the blue team's composition and their skill level.
The argument is that blues must have crits to compete against reds, as well as the ratio; although ranged weapons should balance it out, I find it to be a weak argument since guards should have better positioning, critical thinking skills, and situational awareness when reds rebel.