I think you give the conservatives too much credit. They legitimately think that giving police/MI5 these abilities will tackle terrorism, and that the downsides of these policies are being exaggerated by internet companies/experts and that we're simply not willing to make a golden key because it's expensive/a little hard. They also think that the relatively small impact of terrorism is worth a far more impactful cost.

The scariest thing about this is not the proposals but the wilful ignorance of those in power.