The thing is that "terror" is an extremely vaguely defined concept, in the US there are at least 8 different, and recognized, definitions for it [0]
Nor are there usually any efficient checks&balances in place to make sure these tools are actually only used for their originally declared purpose.
That's why the mass-surveillance creep, since the Patriot Act, has been very real and for the most part completely unchecked, FISA court just rubber-stamping anything that comes their way.
In that context I'd rather see resources put towards fixing vulnerabilities, instead of leaving them open so they can be exploited by intelligence and police agencies. This approach would also prevent much more "evil" than hoping how the "good Big Brother" will not abuse his power and instead solely use the same vulnerabilities to stop the "evil" guys.
Look I see that there is more evil than good done with this stuff, but it's not the stuffs fault.