You've got to get mad!
www.pcgamer.com
I disagree that every single player RPG should have free respecs. I think respecs being limited and having a cost have a similar function as, for example, inventory carry weight: it's a way for developers to indicate to players not to spend too much time doing stuff that isn't fun, because of the tendency of players to optimize the fun out of their game. In Skyrim you're not supposed to go around picking up every loose item you come across, it's not part of the intended game design, but there are definitely players who would do that just for the little bit of extra gold they could get out of it. Similarly, if you can respec at any time without any cost, the optimal way to play becomes to respec before each and every fight to pick the perfect perks/skills/attributes, making the game much more tedious. Developers would then have to choose whether to balance the game assuming all players respec before every fight or risk fights be far too easy for the players who do choose to respec every time.
For example, RPGs often have perks/abilities/skills that do extra damage against a certain type of enemy. However, if you can respec whenever you want, developers will have to assume that players are going to take that specific skill every time they encounter that specific enemy type, at which point you might as well not include the ability at all and just make that enemy type slightly weaker. You could make speccing characters before each fight a major gameplay mechanic of course, but you don't want to do that for every RPG.
Instead of free respecs, I would prefer an (unlockable) option for an advanced/accelerated start to help with the fact that playthroughs often take far too long to do one with every build. Let me skip the (often boring) start of the game and give me some levels for free so I can try out different builds. The more options available for fine tuning your progress for the advanced start the better.
Of course, talking about options, it wouldn't hurt if single-player games would give you the option at the start of the game to allow free respecs, for those players who do prefer to play that way.
EDIT: One more thought: if you discover halfway through the game that your character build is useless, the game has (probably) done a poor job of explaining how to properly build a character. It shouldn't be a matter of trial and error, where the trial period takes dozens of hours and the consequence is starting from scratch. Allowing respecs would just be a bandaid, not a proper solution.