I go to put two brand new lower blades on my CX2 only to find that the holes, where the rotor head pins go in, are sealed with plastic (reminiscent of a broken rotor head pin stuck in there, except it doesn't come out!). I check the package and it turns out that 3/4 blades in an unopened package have this... issue as well. What is going on?

contact Horizon and tell them, they will/should send you new pack for free. Take them back to your the hobby store.
I've never had that problem... yet, Just make sure to check them before you buy them.

Yeah just send them back, from what ive heard from horizon there are pretty good over there.

Im using horizon UK and am not impressed with them so far, no spares in stock, not good i havent flow in 3 weeks now [:@]

But the USA HO orizon are really good