It's not encoded though, your user ID is right there and you can strip it out. I agree that it could be clearer like /question/1234?utm_user=5678 instead of /question/1234/5678

Amazon does similar, along with a generally crap description of the product that isn't necessary, you only need the 'dp...' ID.

The end user viewer can also strip the sharing user ID easily if desired:

https://stackoverflow.com/q/10982911/149428

→

https://stackoverflow.com/q/10982911

→

https://stackoverflow.com/questions/10982911/creating-tempor...

You could argue that SO at least gives you some benefit - there are badges you can earn for popular shared links.

FB also claims their tracking is beneficial, they can show you more relevant ads this way.

Perhaps there are benefits to everything; is the cost, i.e. losing privacy, worth it?

True but the same can be achieved with just asking the person about their needs/interests or using only public data for ad targeting.

Second, this only applies to Facebook users, and yet they also track non-users despite them not even going to be showed any advertising.