This is perhaps a more common opinion than you think. Making it easy to catch bad guys is enough reason. I don't know how to effectively convince someone that the ease of law enforcement comes at the expense of liberty, which so many of the aforementioned opinion-holders also claim to be concerned about. I feel like it should be self-evident, that law enforcement and liberty are mutually exclusive, and that we have things like warrants to allow that infringement on liberty in very narrow circumstances. Dragnet surveillance is warrant-less evidence gathering.
It is self-evident, and they are doublethinking. You can test this by telling them that police should be required to wear always-on body cams. See how they react to that.
> This is perhaps a more common opinion than you think.
Oh, I know it's a common opinion. That's why I'm so upset about it.
> the ease of law enforcement comes at the expense of liberty, which so many of the aforementioned opinion-holders also claim to be concerned about.
Because they're convinced that because they have nothing to hide, the law will never turn against them.