Any particular reason you don't want it? Since you can just use the default FOV and your game play won't be affected.
Can't really think of anything negative that comes with a FOV slider, imo it just makes configuring gunz much more dynamic, for example you can play 800x600 and not get raped to a low FOV or players with a different style like snipers or sprayers can set their FOV to what suits their play style the best.