Is it a hard problem? Sure. Can they get everything? No. But that doesn't mean that they can't quickly act to minimize the total impact. As with many things, 80% of the value can be gained with 20% of the work.
>>wpietr+(OP)
The hard question is whether 80% of the value is available. If you restrict 80% of the worst offenders, but the selection of the 80% is biased in some obvious way, that may be worse than doing nothing at all.