Kind of dilutes the purpose of being a watch list for anti-terrorism efforts, especially if there's too many persons of interest to watch out for. Sounds ridiculous to me.
If it's grows too much, I'd suspect it being a 'big brother' dissident civilian watch list in nature instead. Considering how blurred the term terrorist is becoming these days, pretty soon (if not alright in some cases) that just being 'unpatriotic' or holding a different opinion from status quo, could become falsely synonymous with 'being a terrorist' in people's minds. It seems to be heading in that direction, where freedoms are secretly being destroyed by the guise of 'protecting' the people from a 'stealthy' threat.
I believe that nothing should ever mean sacrifice the vital freedoms like speech, expression, protest, religion, etc you have for government 'protection and security' measures, otherwise you're led into the inevitable police state over time. Problem is most of the time, it happens so slowly, people become psychologically conditioned to think they're still free, when in reality, they have lost aspects of their true freedom already. Usually it's like a brick wall, the freedoms get eroded away until the truth reveals itself, and then suddenly you think to yourself, "What happened?" and realize the reality when it's too late. How does that related to this subject? Well, a watch list of this gross size, is usually the potential beginning of such degradation of freedoms, if it starts to be abused for multiple purposes.