Pros and cons of personal messaging.

Question

As learned from why users cannot send private messages to each other? personal messaging is currently disabled, but OTN staff apparently hopes to enable it in the next two weeks for users who are following each other (it probably means based on accepted Friend relationships).
For what it's worth, here is a list of Pro's and cons, including suggestions and alternatives collected from the mentioned discussion.
Unless there is anything wrong with my collection of cons, I cannot see or think of any pro.
Cons
Pros
A PM requires the prior acceptance of a Friend invitation to protect from spam and unsolicited messaging. It does not protect from unsolicited content.
OTN is as a safe and trusted environment and PM may attract or increase the risk of manipulation or fraudulent activity.
PM falls under the jurisdiction of OTN and can therefore be abused to challenge a victim to break the terms of use.
Rejecting or ignoring a Friend invitation could be considered personal and rude.
PM is not possible if someone does not qualify as a Friend, which can restrict personal messaging based on personal status and spoil the use of the feature.
PM may attract to solve technical problems on a private basis outside the public view and thereby defeat the purpose of the community.
Suggestions
Alternatives
Ability to enable or disable PM or Friend invitations on a general level in the user account preferences. A requester should receive a notice when such a feature has been disabled on a general basis.
Provide an optional email address field in the user profile, different from the login name, where people can find and expect personal contact information.

Answer 1

Dude, you list all those things as Cons, but many are purely subjective views of your own.
1.A PM requires the prior acceptance of a Friend invitation to protect from spam and unsolicited messaging. It does not protect from unsolicited content, though that is the same as any interaction on the internet.  Whether you consider this a Con or a Pro is purely subjective.  The need to be 'friended' first before being able to PM, provides a level of protection from unwanted PM's.
2.In rare cases the ability for people to PM may result in people manipulating others or using it for potentially fraudulent reason, however in most cases, like any other forum with PM features, it's just used by people who want to share something with a friend privately.  The risk of manipulation and fraud is not proven to be greater through PM than through any other interactive media.  The requirement to 'friend' before PMing allows people to only receive PM's from people they feel they are comfortable with, and if they don't like something they have the ability to 'unfriend' and prevent further contact.
3.If people feel they are being abused etc. via PM's they can raise their issue with the moderators/admin who will no doubt be able to look into the issue (or certainly admin should be able to)
4.Rejecting or ignoring a Friend invitation could be considered personal and rude by some people, but then anything people say on the forums can be taken by some to be rude.  That's a personal subjective opinion, and the same anywhere on the ineternet.  Just because a person believes it doesn't make it true.  As taught in Buddhism, a person does not make you angry, the anger comes from within yourself.
5.Just as easily, the use of the forums could be 'spoiled' for people contantly receiving unsolicited PM's from people, if they didn't have to 'friend' them first.  The restriction to just allow PM's for friends, allows individuals greater personal control over who they wish to be in contact with.
6.If people didn't have to 'friend' first then yes, some people would certainly try and use PM's to contact experts or others to try and get their technical issues solved off-forum, and even with the friend restriction, there's a possibility that some may still try that.  The individual, however, has the choice to ignore such requests or reply to tell the person to post their issue on the forum, or maybe they're happy to provide free private support... that's a personal choice.  I can't imagine most experts will be happy to just deal with people's issues off-forum (based on previous years on the forum where people have requested experts email addresses and be told to just post their issue on the forum).  So, PM's could certainly 'attract' the idea that people can try and get private support, but those people are likely to be newbies and would most likely be told where to go.
However, I do agree that your suggestion would be a feasible option, allowing people to choose whether they wanted the friend and PM features enabled via a profile setting, though I do sense you are over-reacting (meant nicely) about people may consider it rude to have their friend request ignored/rejected.  The ability to accept/reject/ignore friend requests does act as a kind of, more granular, method of enabling/disabling the PM feature... you get to choose who you want to have it enabled for.
As for the forum rules, that's a good point, and I hope moniquevdb-Oracle and her team will consider setting out the rules, not just for members, but also for the moderators, so that we can take on board any reports of abuse etc. and know whether they need raising.  Certainly, a common rule on most forums in respect of PM's is that private messages are private and should not be posted on the public forum, and usually  only the site administrators have access to look at such messages against individual profiles where a complaint has been raised.