I have a much bigger problem with the Stempniak and Liles deal than I do with keeping Eriksson now that I've had a bit of time to digest it.
I understand not wanting to blow up the team, and considering Loui a "rental" means they paid whatever the best offer is they received in order to keep him. Whatever that was, Loui is more valuable to the Bruins than any other team, and more valuable than any other rental would have been. He's familiar with his teammates, the system, doesn't have to move across the country, etc.
With Loui, the Bruins have an outside chance of winning the cup. Any team who makes the playoffs has a chance of winning the cup, especially with an elite goalie like Tuukka. Let's just agree with Vegas and say they have a ~6% chance of winning it all. It's not great, but they have a chance. I would think losing Loui would move the needle down to ~1%, and there would be a significant chance of not even making the playoffs. I don't agree with the decision, but I at least can understand trying to avoid the latter situation.
Throwing away 4 middle round picks for two guys that barely move the needle is what really bothers me. The goal of a good NHL GM, in my opinion should be to build a team that can contend every year. The expected value of a 2nd, 3rd, 4th, and 5th round pick is probably a 3rd liner who you have for cheap for a few years. Which is way more valuable than a 3rd liner for 2 months. It's going to actually contribute to them being a better team, more likely to win a cup, over multiple seasons.
edit: (pretty much what shaggydog2000 said in a lot more more words)