No not normal, but the inserts are cheap to replace, or if you call the rifle parts supplier/ or manufacturer if a complete build , chances are they will just send you a whole new extractor spring with insert instead.
As for what the insert is doing, it not so much to add spring tension, but to keep the spring from collapsing sideways as it being compressed.

Being that you can pick up a Colt M-4 extractor spring with insert for around the same price as the insert itself, if you need to buy a insert, then just pick up a new M-4 extractor spring with insert instead.

As for your insert, it was damage when it was being installed in the spring to begin with, so don't freight thinking that it was something you or the rifle did to destroy it in the first place.


Also a quick note, long time ago, the insert color was just a marker for the tension on the spring.  With Colt, the Blue insert designated that the spring was standard tension, and the black insert designated the spring as the stronger tension M-4 spring instead.   Along came other suppliers, and since they did not hold to these standards, you can end up with all kinds of spring tensions with different colors inserts.  I bring this up, since unless you are buying a "Colt" extractor spring, it having a Black insert does not always mean that its the stronger tension M-4 extractor spring to begin with.  



As for the military, since there are two different springs, they just stock the GSA M-4 spring as replacement springs for all the rifles now; which even FN uses that tension spring for the M-16 new builds as well.

As stated, I just tend to pick up the Colt M-4 springs so I know what I am getting in spring tension to begin with,


GSA,
http://www.gsa.gov/portal/content/103940

So with USN number, you can order the parts from GSA at huge savings,  if an approved buyer of that program.
How much of a saving, to give you an idea, a gallon on CLP (ROYCO® 634) is only around $24 through GSA.

Don't use a D fender or O ring with a Extra tension extractor spring.
The tension on the extractor will be too great for the extractor to slip over the rim case at loading in the needed fashion, and instead, either bend the case rim forward as is trying to climb over, or ever prevent the extractor from slipping over the rim and locking the bolt up on a sluggish cycle as the rig starts to fouling slow down instead.



So O ring or defender on a standard tension spring to turn it into a extractor tension spring, your fine, but not with  a extractor tension spring to dam near spring pressure weld the extractor so it can not open up when needed instead.


Also if you have not figured this out yet, the AR does not use the extractor like on a mauser rifles for controlled feeding.
Hence the AR  extractor does not lock on the rim until after the bolt lugs has started to enter the barrel extension lugs instead.

https://youtu.be/GZZphk6JWfQ

Supposed to be incredibly tight,  hence so you can pull the extractor pretty much in the dark of night to clean the weapon, and not worry about loosing the extractor spring off the extractor.

As for installing them, I just use a pair of pliers between the top of the spring and the bottom of the extracgor to crush down on the spring to drive the large coil side into the extractor so the large coils seats in place.