First of all, I don't agree with the decision. Second, I don't like McHale's posing of "we have 2 starting PG" crap. If he's already made the decision, just be confident and stick with it. It was his call, so just own up to it.
Now, that being said. There is some merit to have Lin coming off the bench. It's actually less about defense, but mainly because of skills overlapping. Obviously, Harden is a ball dominant shooting guard, and a very good one. His ability to draw fouls is incredible, and I don't agree with some of the opinions here that Harden is just a chucker with low efficiency and accuracy. Whenever Harden is mentioned by some here, it's always associated with the word "ISO". That's not true, and actually ISO is not such a bad thing as face value of Chinese translation implies.
Let's be honest here, the dagger 3 Lin put on Calderon facing Raptors, at the peak of Linsanity, was a perfect example of pure ISO. Don't we all love that?:) Lots of times, Harden has the ball, but also uses the picks and other players' moving without ball, to create space and lane for himself, and he either shoots or attacks the rim. Those are normally good shots. However, there are times, he holds the ball for too long, and defenders don't even blink facing his fakes. That's where he gets himself into trouble - either forcing a 3 awkwardly or giving up the ball at last second to his teammates. You want to kick him when that happens.
Lin, on the other hand, some of his skills are similar to Harden's - the ability to create for his own, attacks the paint, dangerous in PnR situation, etc., only Harden does that better. However, Lin has one thing going for him, that is his vision and play making skills. But the problem is, he's NOT great at it, not yet. His ball handling skills and shooting (improved during the off-season), prevents him from being the undisputed play maker.
Lin IS a better player than PB, you shouldn't doubt about that. As I mentioned many time before, don't get too caught up with the so-called "competition" with Douglas or Beverly. If you are really worrying about that, you should be happy that Lin got a big contract and be done with it. Until Lin gets better at shooting and ball handling, there will always be talks about whether the backup would "fit" the starting line up, aka James Harden, better. That's not necessarily fair, but it's just reality.
This is a guard's league now, meaning the guards who can shoot the lights out will get the most say. Things like vision, ability to direct traffic etc could be "intangible", if they cannot be transformed into points directly. I absolutely agree with all the discussions about "Playing with Lin, Harden gets better efficiency" or "With Lin at PG, role players are getting better utilized", but this is a star-oriented time. First and foremost priority of a team is to maximize the star power, and that's also a proven winning concept. Team ball is great, but you can't overplay it. Without a legit star, who can attract defense whole night long, your role players won't get many open looks, and they won't be utilized. People bragging about Piston's "team ball" always neglect the fact, that they had 4 all-stars and one near all-star to play that team ball.
You see the complaints about "everyone wants to be PG" etc, and itself isn't really wrong. Point forward Webber or point center Divac did great jobs to direct offense from time to time. It doesn't have to be like Chinese chess, that everyone has to follow exact rules to play whatever is allowed. Pretty-face Chandler Bang did let the hype get into his head, so he was forcing it in game 1. His teammates/coach, and Lin included, have all directly or indirectly criticized him. Players are not blind either. I think Lin's attitude is quite right - as he’s reiterated many times, he wants to focus on his game and own playing, not worried about starting and playing time. Indeed, those things will be taken care of by itself, if Lin can elevate his game.
It's not fair and doesn't feel right, that Lin is moved to bench, after having started 82 games last season and helped the Rockets get into playoffs. But the decision has been made, you cannot quit and go to another team for an interview in NBA. Lin can only keep improve. People thought Asik was in the same boat as Lin is, and with Howard onboard, it's even a lot more logical to put him on bench. But you can't teach size, big men get overpaid in this league. Guard's league also means there are tons of average guards. With Asik's size and skills, he's in a much stronger position than Lin is - there will be teams lined up to get him with this price. That's why his displeasure gets taken more seriously, hence the twin tower experiment.
Lin OTOH, as long as he's not actively sought after, there are always legit arguments that bringing him off the bench benefits the team and himself.
Please don't turn this to a PB vs Lin thing. PB did nothing wrong by playing hard. I saw posts expressing Schadenfreude over PB's injury on the Internet. You can't control what people think/say, but things like that doesn't reflect well for Lin.
Lin is back to starting line up again, after 10 mins of the new season. I hope Lin can keep his cool and play terrific games at both ends of the floor, while he's having the chance. If his improvement over the off-season is big enough to show the world that he can get Horward involved more, and move the offense without limiting Harden, while shooting/attacking effectively, there will be no reason that McHale takes that away from him again. I know it's a tall order, but I have confidence in Lin.