I find this increadibly dangerous. Does that mean the police will move against "potential" crimes? Against people making plans? I hereby jokingly declare that I am planning to steal a cucumber at my local supermarket. Does this make me a goal of preventive action? Did I commit a thought-crime?
1984 and Minority Report come to mind when people say stuff like this.
But where does it stop? If, hypothetically, children raised by a single mother are more likely to commit violent crimes, then it ought to be illegal to be a single mother. That sort of law, which seems crazy, seems to be along the same thought process of why you shouldn't use your cell phone while driving.
So the right to a family life (to use the EU term) is held to be very important, and thus the bar to sterilisation/removing children is really high. The right to use a phone whilst driving on a publicly maintained road is not. Especially as the public's right not to have a 1 ton+ vehicle travelling at speed driving in an impaired fashion is quite important.
Plus it is about mitigating harms. Handsfree kits are allowed for example.
The exact thing happens in this case. His right to be silent or have a lawyer present is not infringed. His right to be informed whilst being asked questions relating to public safety about future threats is being infringed, because society shouldn't have to choose between future potential victims and prosecuting an individual for crimes already committed.
Edit: Your claim that this is limited to mainly English speaking countries is not even true.
"Most nations prosecute inchoate acts (such as conspiracy and incitation) in their domestic criminal law."
https://www.law.upenn.edu/journals/jil/jilp/articles/1-1_Ste...
Attempting to commit a crime is also a crime in many jurisdictions, and only requires one person - maybe a prosecutor could convince a court that Derbasti was going to steal something, as demonstrated in a HN comment, but the plan was foiled.
Also, perhaps it is a threat - if other comments could be used to show that he/she was threatening the local supermarket unless they do something, perhaps charges for threatening could be filed.