Not at all. I apologize if it sounded that way.
I don't agree with his recommendation of port forwarding, unless things won't work any other way. SIP scanners are extremely prevalent - operated by hackers looking for unsecured VoIP equipment they can use for personal gain or criminal activity. If your VoIP equipment rejects such calls you may never know you're getting scanned. The attacker however does know your equipment is there, and will keep attempting to crack it for an indeterminate amount of time. If on the other hand your equipment is behind a "restricted cone NAT" router with no port forwarding or DMZ, there will be no indication that your VoIP hardware even exists. I would never say that something is completely "unhackable", but that would be as close to unhackable as you could get.
If a user's router is such that port forwarding is absolutely necessary, then a high SIP port (X_UserAgentPort if you use an OBi ATA) between 20000 and 65535 should be used. Most SIP scanners scan around port 5060. While using a high SIP port does not make you invulnerable to the scanners, it makes it less likely they will find you.
If you do remove your port forwarding, the primary issue to watch for is that you're still able to receive incoming calls. Whether or not the SIP port is forwarded will not affect, for example, audio quality.