As someone already pointed out, silliness on the WWW is not difficult to come by. There is already enough silliness to go around. But seriousness seems to be a rare resource. We should do our best to preserve what little of it we can actually find, lest serious thought become an extinct activity.
Silliness is often something of a default activity. It requires little or no effort. If one starts a thread with no meaningful content, it is not likely that there will be any shortage of replies with no meaningful content.
On a forum like this one, threads remain in existence indefinitely. If someone starts a silly conversation IRL, the silliness ends when the conversation is over. But a conversation on an online forum need never end. Serious discussions require a constant stream of intellectual fuel, a supply of food for thought; if there is no such supply, the conversation stops. But silly conversations are self-sustaining. They behave like chain reactions. Once a silly, pointless thread starts it is unlikely to stop of its own accord, and it will encourage others to form... and the next thing you know, the only thing happening is word games. There is a negligible risk, if any, of anything being overrun by a sudden outbreak of seriousness. But on a site like this, a sudden outbreak of silliness can spell doom for intelligent conversation.
That is not to say that silliness is bad, or anything. It certainly shouldn't be stamped out entirely, but too much of it could be a problem, and there is a definite risk of too much silliness.
I see no point in segregating these two types of activities into separate sections. Having a silly section is just asking for it to be filled and to overflow.
I intend to say more on this topic later, but now I think I'd better get some sleep.