You say dragnet searches are rational, but your only rationalization was that "inveatigators need to do their job." That seems like remarkably lazy thinking. We have limitations for a reason, everything from separations of powers such as judicial review/warrants, to natural rights such against use of physical of force, property seizure, to privacy rights, etc.

Just saying this is rational because investigators must do their jobs seems entirely ignorant of the obvious, implicit balance of powers issue here between free peoples and government authorities.

In short: There are, in fact, good reasons most civil liberty organizations fight against dragnet searches. It is not an emotional hunch.