So no, your argument doesn't make any logical sense.
It's my opinion that in any reasonably developed and old democracy a majority of the population are currently criminals in the sense that they have broken at least one law.
In reality, that law is either trivial, inconsistently enforced, or generally ignored. But the important thing is that it's still on the books as the law of the land, and therefore makes the citizen prosecutable in a court of law.Whether or not that individual is prosecuted then becomes the folly of most systems -- a choice that can be arbitrarily made (as it's never incorrect for the government to enforce its current laws, even if it can be unjust).
As a consequence of all the above... pre-investigation is tantamount to power-to-convict. And privacy is the only effective deterrent against "I would like to find some crime you're guilty of and then charge you with it because {unrelated and non-legally-based rationale}". Imho, this is the fundamental and most dangerous type of corruption a democracy can fall institutional victim to, because it only requires that there be a large number of rarely-enforced laws on the book (a systemic weakness of democracy where repealing a law takes more effort than leaving it valid) and individuals of questionable motive (human nature) in positions of power.
(I'm perfectly willing to accept that others may have a different viewpoint on democracy, but I think I historical support as to this is the actual way a mature legal system functions)
In countries where legal expenses are high and punishments are sever (i.e. the USA) it can be trivial to find something damning enough to put someone behind bars. In countries where the bar for prison sentencing is substantially higher and legal costs are more manageable the most authorities could do is waste someone's time. This is one of those aspects in which societies the world over markedly differ.
In a completely transparent system, you'll still have bad or questionable laws. You'll just have them only applied to people who can't buy their way out.
Unless complete transparency also solves the corruption problem. ;)
If privacy is a human right that cannot be violated ever, how are going to deal with criminals that use services such as WhatsApp?
By finding evidence that does not rely on services such as WhatsApp. How did anybody ever get convicted before the age of WhatsApp, or for that matter the invention of the telephone. It's not as if wiretaps and cell phone messages are the only kind of incriminating evidence that can be found on the vast majority of crimes. And if that is the evidence that stands between a free man/woman and their conviction then maybe it is better that they go free because it is all too easy to forge such evidence or to plant it.
A nitpick, but I really dislike this line of reasoning. Before WhatsApp criminals communicated using different means which were easier to monitor. Now that they have WhatsApp (or whatever), they will use that instead of easier to monitor methods. A move to modern communication tools gives them an edge over law enforcement, so it's no surprise LE feels a pressing need to do something about it. It's an arms race.
Perhaps sloppy criminals did so, but the careful were engaging in schemes more like what we see on "The Wire". Meeting in secluded, noisy locations wherein privacy was all but guaranteed.
People, including not-convicted criminals, have the right to privacy. If the NSA and law enforcement are going to make it harder and harder to find private places through dragnet collection, it should not be surprising that the populace will seek to reclaim privacy.
If it's an arms race, as you say, it's an arms race that law enforcement was winning at so one-sidedly that the relationship was becoming abusive. Tools like WhatsApp, Telegram, Signal, etc., are the citizenry's first efforts at serious competition.
And lest you think that this is only a problem with China, America has the exact same issue. The FISA court was supposed to hear requests for people's private info but it was a glorified rubber stamp, granting 99.9999% of requests. And that's the problem, you cannot have a free and vibrant democracy when people's privacy is negotiable.
Perhaps that sounds like hyperbole, but have a look at what other commenters are saying about fishing expeditions and tell me if you still think so.
After someone is convicted, there's no use on wiretaping him about something that was already solved.
How simple is it to make someone an alleged criminal, well, that's country specific. Can also be thought on how easy is to have a government receiving data directly from Facebook, or using gag orders, or bombing another country without proofs of any wrongdoing.