Back to the parental comment - it's been decided there isn't really a good reason to have most guns and so they are strictly controlled - I mean what's the legit reason for having an assault rifle?
Now if the government thinks there isn't really a good reason to have a phone they can't hack ( because they are the good guys right.... and in theory need court orders etc - so there is legal oversight ) then they will see such phones in the same light and consider banning.
This is at the core of the argument - and why governments ask for a special backdoor - as they accept a generally secure phone ( to stop your neighbour snooping ) is a good thing, but they are used to being able to tap phones and open letters if a judge gives them permission.
Obviously the ironic thing is most phones probably already do have special backdoors - but only for the country where the makers reside - and that countries government doesn't want other governments to know or have acccess.
And in the case of fridges - there is no argument there that they aren't legit reasons to own.
In the case of knives - zombie knives don't really have legit use, whereas kitchen knives do.