It looks to me like the primary use case SyncThing is built for is to keep all nodes in sync with the latest global version of your files. For most users in most cases, a fully-connected network is going to be the most effective way to do this. If that’s the case, than shouldn’t the “Introducer” feature be on by default, and only turned off if a user has a specific, unusual use case where they would prefer it to be off?
As it is, there are no privacy concerns around the “introducer” feature, because the data about other nodes is shared anyway, whether it’s used or not. So the only “downside” to having introducer on is that it creates a more fully connected network, which is almost always what the user actually wants, right?