I don't think people are generally making fun of Linux just being a kernel. What I think is generally happening is Person A starts to compare Linux and FreeBSD and Person B comes along and says how the comparison is wrong because you are comparing two different things: a kernel vs a kernel+userland.
At best, Person A uses Linux to mean GNU/Linux but Person B is still just pointing out that GNU/Linux is a collection of projects developed independently† and integrated together, while FreeBSD is a system that is designed as one (though it does have a some third party components: e.g. ZFS when we switch to the new OpenZFS).
† And by being developed independently I mean that GNU software is developed to run on a number of kernels, and the Linux kernel is designed to provide for a number of userlands. The two happen to be a popular combination, but they are not designed for each other.
