In reality the same arguments apply to adults, but we find it less morally repugnant because adults aren't innocent and are expected to gaurd themselves against such actions. However, it becomes more and more difficult to guard against.
This seems like a very mushy reason. I'm pretty sure the real reason is that children are not considered able to knowingly consent to many things - including contracts such as EULAs or TOS. Given this, a child is also not expected to be able make a reasoned decision about privacy tradeoffs.
The reason it's "ok" to spy on adults is that they can make an educated decision about whether they're ok with being spied on. I don't necessarily agree that this is true in practice, but I think that's the theory.
It should also be completely illegal, but the justice system can't keep up with technology. Imagine you found out that your next door neighbor has drilled a hole through the wall and fed a camera into your house - what do you do? (Call the police, certainly). Is it really any different when the camera feed isn't a physical wire but done over the internet?
That's wishful thinking. Most people can't tell the WWW from Facebook. People are so bad at writing emails that there are Workshops for Composing E-Mails which sell out quickly. Many disable SIM PINs because they forget them or don't want to bother remembering them. The people who read permissions an app requests make such a little percentage of smartphone users that they can't even be considered a minority.
I beleive we need some kind of CE for software. It's easier to make sure that your parmigiano reggiano comes from Emilia-Romagna that it is to make sure that you can rely on a certain online service provider / platform. That's simply unacceptable.
Most of them don't care.
Yes, and hardware at the firmware level.
We generally believe that sexual exploitation of children is worse than of an adult. We don’t allow for consensual sexual relations, creation or mere posesion of explicit material with a child.
In fact drawings of said material can get you in a lot of trouble in many, liberal, countries.
That being said, I hate what the internet has become.