I remember you once replied in one of my comments in your post that there are some particles that are their own antiparticles; if I'm not mistaking. But in this case, would they have opposite quantum numbers?

Everything you said is correct. And the only number who is its own opposite is 0. Therefore, in order for a particle to be its own antiparticle, it has in particular to be electrically neutral.

This was not a stupid question! :)