I understand what you're saying in general, but I'm not sure how the design of a game is changed by the inclusion of respeccing. Nobody is going to build a game that specifically encourages it. Or are you arguing that it will make the developers lazy and not bother to balance the game for all classes / builds?
If an option is in the game, people are going to use it. If people use the option, it's going to change their perception of the game. It doesn't really matter at that point that the developer doesn't regard it as a vital part of the game design because he only included it as an "emergency button". To the contrary, the inclusion of the option might actually signal to the player that he
should respec often in order to have a good build for the different areas of the game. Thus the game could become known as "that RPG where you have to respec all the time", even though the option was included with the very best intentions.
But I absolutely don't think that this is a reason not to include respec. I actually think it's a very important feature to have. Immersion is important in an RPG, that's true and I am not arguing against this, but immersion isn't more important than the "enjoyability" of a game. The most frustrating thing that can happen in an RPG is to realize after 15 hours of gameplay that the character you build is useless.
And I absolutely don't accept that this should be regarded as the player's fault.
In most cases, the player couldn't have known before hand. Most RPGs demand you to build your character in the first minutes of the game. It's at the very beginning that you have to decide who you want to play for the next 30 to 100 hours. But even though there are theoretically dozens of viable combinations, it's nearly impossible for a game to support all of these combinations viably. Even if a certain character seemed to be great and fun in your mind, it might turn out that this particular game is designed in a way that renders your character useless.
How would you have known that? You didn't experience more than 10 minutes of gameplay yet, how could you have known what this game expects from you?
I agree that respec shouldn't be encouraged at all times (and it doesn't make much sense to change your character after 50 hours of whatever), but it should be there. Limit the amount of possible respecs to, say, two times. Make it expensive (but not so expensive that the player who needs it can't afford it anyway). Make whatever you can.
Respec is only one solution, though, and it should be the last. More importantly, I think that RPGs need to be more transparent upfront. Analyze my build and tell me: Is this build viable? What do I have to expect? Will the game be really hard with my specs or is it going to be a cakewalk? I'm aware that his is easer said than done, but I think it's a very important step to take.