Why is List not thread-safe?

Question

From the following site:

http://crfdesign.net/programming/top-10-differences-between-java-and-c

Unfortunately, List<> is no

Answer 1

Why would it be thread-safe? Not every class is. In fact, by default, classes are not thread-safe.

Being thread-safe would mean that any operation modifying the list would need to be interlocked against simultaneous access. This would be necessary even for those lists that will only ever be used by a single thread. That would be very inefficient.