Exactly. You boo everyone and IMO every fan has the right to boo whoever he wants. Here in Europe, every team in every sports has its group of die-hard fans who usually sit behind a net (or a basket). They use drums, make noise, sing all the time FOR their team and also AGAINST the opposite team. And insulting a player/his mother is not uncommon at all. I'm not saying it's right or not, but I'm used to this and all the hype surrounding the "To boo or not to boo Blake" seems to me a bit strange.
I just want to tell you a story...
Now AC Milan is arguably one of the best 5 soccer teams in the world, but in the early 80's things were a lot different. During the 1981-82 the team went down to Italian 2nd League (Serie B) and during the Summer the richest teams were after Milan's 2 brightest stars, 2 young defenders: Franco Baresi, the team captain, and Fulvio Collovati. These teams were offering a lot of money, and simply Milan couldn't afford them. The 2 players took opposite decisions: Baresi, who was the best among the 2, decided to stay, he said he didn't mind about the money and he didn't want to betray the fans who loved him so much. Collovati, on the other hand, said he was too good to play in the Serie B and he wanted to win something. But he signed for the worst possible team, with Inter Milan, our arch-rivals. From that moment, every Milan fans started to hate him, to despise him. The funny thing is that Collovati spent 4 seasons with Inter, then was traded to a lower team and shortly after retired. He never won a F***. Franco Baresi won something like 5 Italian championships, 3 Champions League and some other trophies. He called it quits at the age of 36, the team retired his number and he held a farewell game in which all the world stars played.
I remember every time I was at the stadium and we played Collovati's team, every time he touched the ball it looked like the stands were falling down for the noise (85,000 fans can make a LOT of noise...). To make you better understand the atmosphere, it happened that after a play he fell down in pain, grabbing his leg. The whole stadium, also kids, old men, women were singing while clapping their hands "You must die".
The Kings didn't offer Blake peanuts. He wanted to win something and he made his decision. I'm fine with it. And I'm fine with him being booed, I don't see anything strange about that. It's part of the game.