Appealing to the audience
The trick that politicians are pulling again and again is appealing to the audience. Rebuffing expert criticism is an integral part of this tactic. The speaker makes then connection between A and B (here end-to-end encryption and terrorism) so that any criticism is perceived by the audience as an attempt to undermine security. Amber Rudd almost certainly understands the oxymoron of end-to-end encryption with a backdoor but she knows that her audience almost certainly doesn't. If she aligns herself with her audience any criticism of her arguments will be perceived as criticism of the goal – greater security – and those who want it.