I don't play FPS, but I can understand the criticism, I guess people don't like having their options blocked. especially in games that are "one man Vs EVERYTHING!!!!".
I want the ability to mow down enemies with a SMG after throwing 300 grenades on them and shooting them from afar with a sniper rifle. why take that away from me?

some weapons are fun to use but not necessarily practical (like a reflecting beam, or a freeze ray that lets you break your enemies afterwards), and if I have to go with only 2 weapons, I'm not going to get the chance to use them.

it's especially relevant in single player game, if I would want to make it more "challenging", I'll do it myself.