As with any academic question there are valid arguments on either side of the debate. Having read around the subject, one issue I notice coming up a lot is anonymity which I believe links into the question at hand.
Possession of multiple online identities allows for a level anonymity, something that can be argued in this technological age is something that is valuable when used sensibly. Christopher Poole, creator of the website 4chan (an entirely anonymous forum), talks about how websites like Facebook are eroding our online options as you may possess only one online identity. He says that you should be able to present a different identity in different contexts and be able to express yourself without risking a permanent stain on your identity, something that having only one online profile doesn’t allow for. Something which I agree with to a certain extent, I value my privacy and do not necessarily want colleagues to know every detail of my personal life, hence blurring the boundary between work and play. This is why I have a Facebook page for personal and a Linkedin page for professional. The work of Costa and Torres (2011) talks about this dilemma too, saying that one of their participants had a different online identity for each service she was experimenting with as she didn’t want her online self to be a snapshot of her real life self.
On the flip side of the anonymity argument is a much darker side of the coin. Granting the ability to create multiple online profiles leaves the internet open to abuse, due to the ability to remain (semi)anonymous. Owning multiple online identities allows for malicious content to be created and broadcast in the form of cyber-bullying, trolling, spam and unfortunately much more. However, although these are a plague on the internet, they are still manageable by the right people if things do get out of hand. In which case, I am of the opinion that being able to own multiple OIs outweighs this disadvantage. A further point against I read recently made by Chris March on the Epiphany blog is that nowadays people’s multiple online identities are often linked. This means that if one is hacked, it is very easy to gain access to the rest of them and identity theft can occur, although again this is manageable and preventable with safe browsing practises.