A couple of more thoughts why spoofing is bad:
1) If you have a dial in voice mail system you now need to have secondary password
2) If you set up a custom voice mail or outbound ringtone for a person and someone spoofs the number they hear that message
3) It is too easy for a Visher (voice phishing scammer) to call up and impersonate a bank and gain access to your personal details.
Got any others? Post them in the comments!
Spoofing for reasons of deception is obviously bad and violators should be prosecuted by the law.
However, just because one “alters” their Caller ID, that is not necessarily spoofing. There are legitimate reasons for altering a Caller ID.
I explain this in more detail in my comments on your VoIP Watch Blog.