@EzekielRaiden:
I will run my games the way I and my players see fit. You, and any other outsider, have no say on that. In attempting to do so, you are attempting to limit my group's agency to do as it wills.
(I suggest everyone answer his objections this way. There's no need to justify to others how you play your game, nor should others request that you justify it, and vice versa. In all cases, it's "you do you". The ultimate agency isn't player agency, nor DM agency, but group agency - every group is allowed to play the game as the group sees fit, free from how others think they should play it.)
I don't believe
@EzekielRaiden really has an issue with running your game how you (and your group) want to, but more about understanding why some DMs would deny player agency for what he might consider trivial reasons.
And for some of us (myself anyway), it is not about "group" agency, either. It is ultimately about DM's running the type of game they want to run. As a DM (and all the DM's I've played with), DMs do a lot more work and have much more responsibility towards creating and running an enjoyable game for the entire group (the DM included!), not just for the players.
If a player want so play a certain race, or use features from a certain book, I (as DM) have the right to veto that choice--for whatever reason. Some might find those reasons trivial or whims, others might not. But, regardless of the reason, if I feel those choices will greatly lessen the enjoyment I have from running the game, I won't allow them. If the requests are not as big an issue (they might bug me, but I can live with it), then I'll allow them. But, in the long run, I am running the game and ultimately it is my decision.
Now, if a player doesn't feel I am being fair, or ruining their game, they can voice their concerns. If we can't reach a middle-ground of some sort, they can go or stay as they want. If they stay and begin to ruin the fun for others, I won't invite them back.
However, I (as a PLAYER) will abide by whatever rules, limitations, etc. the DMs I play with choose. My enjoyment as a player (given how little time I put into it before hand) is not limited by my choices of races, rules, or whatever. I can always find something I'll like. However, if (after playing a few times) I realize the DM's
style (yes, italics are great...) don't appeal to me, I will thank them for the game, but bow out and move on--even if they are friends. (And fortunately, we can remain friends despite our differences.

)
I won't ever tell others how to play. I might ask so I understand, but their game is up to them. If I like it, awesome, if not, such is life.