It's a complicated question that presents me with difficulties. Let us assume that we live in a country with separate Executive, Judicial and Legislative powers. Despite failings, this is largely true of the UK. If the executive (police etc) want to spy on someone they need a legislative authority and I would like them to have a second, independent, step by which someone evaluates if the purpose of their spying is within the legislative authority. That would be a judge. I am not convinced that the Home Secretary (which is an Executive position) is the right institution to be conducting this evaluation. A judicial oversight would be more comforting methinks.
I don't have a problem with the state hacking for the purposes of investigation. Placing the existence of this capability into the public domain certainly impacts the probative value of information found on a device (the planting of false evidence becoming likewise easier). This is akin to weight of the finding of physical evidence with the probability of the planting of false physical evidence with the warranted access to a suspect's property or person. Corruption is the problem here, not the means by which it is effected.
What concerns me most of all is the creation of legal processes which are not subject to the scrutiny of public view. It is this issue that should be at the top of all the agitation about the progress of these courses of action. Secret courts or injunctions, the existence of which cannot be mentioned are frightening and indeed so Kafkaesque as to be worthy of new round of parable fiction.