I don't know anyone who is claiming that having a police force is bad, or that all investigations should be illegal. That's a strawman. Unless you can point us to people saying that?

The debate has always been about (a) the effective destruction of the warrant system and (b) the pathological levels of lying that have accompanied it.

Luckily, there exists a design for a system that allows for nuanced collection, as you put it: warrants authorised by skeptical judges who filter out fishing expeditions, combined with punishments for law enforcement workers who try and game the system. It's actually just the old system we thought we had and was fairly uncontroversial.

However the intelligence agencies are not in the business of doing such work. If the old system was rigorously enforced then we'd be left only with the question of foreign spying. Arguably that should just be scrapped in the modern world: the most valuable commercial secrets are all in the 5 Eyes countries to start with anyway, spying on allies makes them less likely to be allies in future, and if you subtract out the foreign wars started by the west you're left with things that seem to produce little real world impact (watching North Korea for instance: what are we gonna do about it, exactly?).