I agree with the other commenter who said that, if the keyword search is narrow in scope such that it would apply to
this particular crime (in this case, the exact address, and timebound), then it strikes me as a "reasonable" search, and not a fishing expedition. Furthermore, it seems pretty analogous to what is required for a warrant for a physical search - you can't put out a broad dragnet, it must be targeted in scope, and the definition of "targeted" has pretty much always come out of case law.
Now, when it comes to the fear about being used to prosecute abortions, that is really a totally separate issue, as doing a reverse keyword search for "get abortion pills by mail" is too broad. But I think the broader issue with the abortion examples is that many people fundamentally believe the laws are unjust and deserve to be broken. Whatever the case may be, the legal system itself surely cannot differentiate between "unjust" and "just" laws.