Bear in mind that no it cannot write arbitrary files. It's a unix system, it has unix permissions, and required privilege escalation to write to locations the user is not allowed to.
Although strictly true, Unix DAC is a security model that stems from the 60/70ies. When a malicious actor gets read (or write) access to your home directory, it is pretty much game over (think cryptolocker, identity theft, loss of sensitive files, etc.). With vulnerabilities in internet-facing software being a fact of life, you want compromises to be restricted to their own little sandbox, not all the files in your home directory.