It may look like I have a huge grievance against snipers, but I don't. A bad player will help little no matter the class.

The player I -really- hate is the one who see a guarded chokepoint, full of soldiers, demos and sentries and throw some bullets / rockets / grenades there, retreat and reload, usually screaming for healing. Rinse and repeat. This kinda of player will be the one who quickly point the need for an uber or more medics.

A sniper doing nothing is just easier to spot, but a soldier shooting the ground near an enemy but hitting nothing isn't doing much more either.