I think the public nature of the lists is a known quantity for anyone using this site- it should become very obvious to anyone setting up an account here that there is no private feature. It might be a nice thing to add, though- let people set their collections to private/followers only. Feature request, maybe?
The few times I've used the collection link under the avatars, it's usually not to sit around browsing their list, but to access their stats page. It's interesting to see the overall numbers and how they compare to other users. Sometimes I do click on a few pages, just to get a feel for what kind of games said person seems to like. Collection photos are more interesting, but tend to focus on console setup & storage choices, not the actual games within.
I think theft concerns are minimal. Of course anyone who broadcasts exactly what they've got could be casing their own joint for a potential thief- but it's a forum board. Fake names, no location data required, etc. As far as digital goes, very little of it is transferrable or sellable. Basically any ne'er-do-wells would have to do a LOT of extra legwork just to figure out where their possible mark even lives. Honestly, it would be a lot easier to just get a job as a home repair man if you want to discretely look for people to steal from.
