We already have warrants, judicial oversight and public audits to prevent abuse of power. Not sure what's authoritarian about standard overt surveillance.
No, not in the UK. XKEYSCORE surveillance tools are used without a warrant signed by a judge (the police grant themselves "warrants" covering unlimited uses for a period pending renewal, which I would have assumed constituted a "general warrant", something prohibited in UK constitutional law... but I am not a UK lawyer).
MI5, MI6, and NCA are immune to Freedom of Information, and you cannot sue in open court; you can take it to the Investigatory Powers Tribunal, who will not even let your lawyer see the relevant information to the case.
Everything you said is true and inteligence agencies should not be above the law. But the logical response to that is to fight for strict oversight, judicial reform, and to disallow the misuse of those tools, not to abolish surveillance entirely. A broken system should be fixed, not thrown away (unless there is an alternative better system which is not plagued with these issues).
This was so profound. Now that I think of it there is nobody to watch the watcher and we should just dismantle society and let the local warlords sort out the crime rate. /s