"I'm not sure whether you did or didn't expect a reply, but the reason no-one has could be that it is simply a stupid question."

Not simply a stupid question at all leveler – How do you gather information and obtain intelligence about those who would do you harm. From what both you and MGOH say, you could only ever be reactive and start after they have struck.

"you make the assumption that there is a justification for having a database of largely innocent people going about their lawful business."

Ever heard of the DVLA Leveler?? What is that if it isn't an enormous database of largely innocent people going about their lawful business, but I can find no great argument against it so it's existence can be easily justified.

There again I walked around with an ID Card for years and didn't find that any hardship either. The degree of objection I suppose all depends upon exactly what it is you have to hide.