SNMP v3 at least has some security in mind, but a lot of devices are just v1 or v2c which are basically unsecured. Allowing ANY write access via SNMP is a bad idea in my opinion, unless you segment it out into it's own secured management or out-of-band network. Even then... I'd be worried.

Network infrastructure security has a lot of unsolved gotchas and not a lot of industry desire to fix. Most of what everyone interacts with is in an abstracted or virtualized layer on top of the old plumbing.