But they do. They use a package manager such as apt-get, that cryptographically checks everything.
Installing software outside the package manager is the exception here, not the norm.
Installing software outside the package manager is the exception here, not the norm.
Essentially, if someone wants to hack your system they will, whether it's patching your routers firmware, etc.
If Iran can't keep stuxnet out of airgapped systems, you're not going to keep any serious actors out of your systems connected to the internet.
We educate users to download software from distributions rather than trusting random sources (that might be very safe or not).
A recent example to add to this, for those who think "nobody who's not a complete beginner would never do that":
https://www.reddit.com/r/netsec/comments/3lefc6/chinese_ios_...