I mean it really does suck to see Tanner Pearson go. I can understand the rationale of it (he's been underperforming the most out of the bunch, even though the team has been horrifyingly underperforming so far this season). It also does suck to trade away a younger player (that was a first round draft pick in 2012) that had shown to perform well in better circumstances.
I mean this was a guy that was drafted the year the Kings won the cup in 2012 at #30. Found himself on the main roster in 2014 and was in a high scoring line-up with another young-and-comer (Toffoli) and a solid consistent goal scorer (Carter) and that line-up was doing a lot of their scoring against the Blackhawks in the playoffs in 2014 (who was pretty darn tough to beat, especially when the Kings were playing them in that time period) and was a vital guy in that cup win in 2014. I'm fairly positive that Pearson will do well with the Penguins and will probably be more upset (at Kings' management more than anything else) if he was playing well and it shows in the numbers at the end of the season.
I've been reading around that Carl Hagelin has his good moments and qualities, but hasn't been showing them that much so far this season, so I don't know if the move will energize him or the deteriorating Kings team, but stranger things have happened, some good, some bad, so let's see.