Here is how I feel about it:
1. Context of use
Are you going to be stabbing the knife hard into wood, practice dummies, meat, ice, or other media? Or, will the knife be used for slicing, dicing, cutting, carving, and related tasks?
If the former, you might like a guard.
2. Context of environment
Are your hands constantly soaked with oil, blood, or another liquid? Do you work mostly with gloves? Or, will the work be mostly in dry environments and held with an unprotected hand?
If the latter, you should be ok with no guard.
In many ways this reminds me of a debate between locking blades (backlock, liner lock, axis lock, frame lock, etc) as opposed to slipjoints.
Just like locks on folders, a guard can be a nice failsafe and could prevent an injury. But it does not make the tool inherently safe. Many people have been cut on blades with guards.
On the other hand, like a slipjoint, using the knife as it was meant to be used with purpose, care, and control should be enough to keep you out of trouble.
Some people use knives with care, and enjoy the safety of a lock or in this case a guard.
The argument may be rephrased in terms of aesthetics. Which do you like better? Which feels more natural? Which will you carry and work with?
For me, I do not care either way, but a little ridge here and there can be comforting.