It is perfectly logical to say that if there was an assault on a college campus and that the victim said the perp is an "Asian male", for the police to not prioritize the questioning of all non-Asians in the area. And if the report was made within minutes of the incident and the suspect is on foot, it may be justifiable to target the 5 Asian males loitering around rather than the 95 people of other demographics. What logical person would argue otherwise?
But the problem creep comes in the many, many cases when police don't have a threshold for how long and wide that demographic descriptor should be used. Within 1000 feet of the reported attack? A mile? Why not 2 miles? And why not 2 days or even 2 weeks after the incident, just to be safe?
The main difference in the ISP/IP metaphor is that in the digital world, it's possible to imagine search-and-question tactics that aren't time-consuming for the police or for the suspect. Hell, the suspect might not even know their internet-records were under any suspicion. OTOH, there are definitely real-world places in which for the police (and their community and most specifically the politicians), hand-cuffing and patting someone down has been so streamlined and accepted by the powers-that-be that it isn't a bother for them (the police) either.
edit: To clarify, I don't mean to get in the very wide debate on racial profiling, etc. But when I worked at a newspaper, we had a policy to not mention race unless the police could provide 4 or 5 other identifiers. That led to readers cussing us out because, they'd argue, knowing that the suspect was black is better than nothing. My point here is that sometimes, nothing is not always better than something, and that is most explicitly clear when it comes to broad IP range searches.