It's part of the thread and thus should be shown. It's not like it would overload the browser or anything. Having to first spot that there is a hidden part of a nested thread ("see more replies") and clicking on it and waiting for it to unfold happens so often, it's bothersome. In my view it's totally unnecessary except for curbing excessively long response chains, but if you do that by, say, hiding level 10 and deeper, it's already closer to the typical end of such a chain. And, after all, plenty of top level responses are loaded on thread access anyway, so no real risk of initial-load-bloat. Should at least be an option to turn this off. It's also annoying if you click on it to unfold for just one more reply.