Pielorinho said:
Imagined this way, no opposed roll is necessary, and it makes perfect sense that higher level wizards would easily know how to cast their spells in the middle of battle while paying attention to their surroundings.
Yes, that is a perfectly reasonable way to imagine what is happening based on the rules as written.
Unfortunately, I am a firm believer that AoOs should be an integral portion of the overall mechanics of the game. They are there to prevent abuses.
Hence, there should be no way (and there is not in my game) to remove them completely.
There are ways to lower the chances of them occurring significantly, but there are no ways to lower the chances to zero (in my game).
I feel that having any immunity to an AoO is a flaw in the design of the core rules. With AoO immunities, characters are able to do impossible things, merely due to the mechanical nature of the segregated initiative system.
For example, Tumbling past the extremely high level guards of the King and stabbing him. In this case, you should rarely be able to do this, not always be able to do this, just because you have +14 in Tumble. The alertness and combat capacity of the guards to defend the King should also be a factor.
The counter "opinion" that "Well, some of those guards should have readied actions prepared" is extremely lame. The only way to protect the King is to have some of them prepare a defense that might not be needed or used and they may waste their time doing it? Hmmmm.
JMO.
To me, AoO immunity is tantamont to having a feat that allows you to decide in every single turn when to go. You can go at the beginning, the end, or somewhere in between based on your whims at the time. In other words, such a feat would be a meta-game feat that allows you to do things that affects the actual mechanics of the system. This is how I view AoO immunities. They allow you to affect the actual the mechanics of the system and are a basic design flaw of 3E. IMO.
To me, casting defensively means that you minimize the opening that you present to your opponents when you are casting a spell and it is up to them to be capable enough to take advantage of it. It is not removing the opening that you present, rather it is making that opening as small as possible.
Other people do not see it that way. I think that if the rules were originally written without AoO immunities (such as Mobility which just gives a bonus to AC), then I doubt very many people would be arguing that AoO immunities should be added to the game (unlike today where some of us argue that they should not be part of the game).