User subscription and permissions says: "Since subscribing to other users can be problematic when taken from a "stalker" perspective, it is recommended that subscribing to another user require permission to be granted." And then a lot of extra features related to this are described.
Nowadays anybody can see the user contributions of anybody without requesting any permission. Why is this different? Is there a problem with stalkers because of this? This feature could be as simple as Twitter's Follow.
If someone misbehaves it's not because of following but because of posting inappropriate content in your user page or the discussions where you participate. After all this years of Wikipedia I guess we have precedents on this and ways to deal with this situation?