That's an interesting stance, you don't care about rootkits? What about malware, which has been found in the wild, which abuses root privileges to steal account information? That malware is extremely difficult to detect directly.
What you're thinking of are things which use exploits to gain root - this may be done by some users, but most often Android devices are rooted via bootloader unlocking these days, which does _not_ use an exploit.
Exploits however are used by malware - and not having your device rooted won't prevent them. They gain root via exploitation, whether you want them to or not.
Not to mention that the kind of root detection done is by looking for things that only the legitimate sort of root leaves behind, like a su binary which prompts the user if they want to permit root or not.
Often times, rooting your device legitimately may allow you to flash a custom ROM and get updates that your original vendor hasn't released for your device, allowing you to actually _prevent_ exploitation by malware, even after your vendor has long abandoned the device.
That'd be some very stupid malware - anyone who was actually rooted would notice immediately when their root tool told them their support binary needs to be updated.