The most common is to participate in signature deals. I know that you are going to say that this contributes to additional spam, and this is probably correct to an extent, however it also attracts additional people to the forum (and to bitcoin) that would not otherwise be here. This overall will increase the adoption of bitcoin and will overall increase it's chances for success.
Having new people just for the sake of isn't necessarily the best idea.
I already countered this point when I said that that people buying accounts for signature deals will ultimately get involved in bitcoin (e.g. buying and spending it - or increasing adoption). Anyone that says that higher adoption is not a good thing looses all credibility in my book. We are now at a point where increased adoption would not potentially harm the network (e.g. we are not in 2010 when having wikileaks accepting bitcoin would attract unwanted attention). As it stands now a very large percentage of the people owning/holding bitcoin are doing so because they are speculating the price will go higher in the future. However in order for demand for bitcoin to increase (and in turn the price of bitcoin to increase) overall adoption needs to increase dramatically. Short of taking advantage of people and breaking the law there is really
zero reason to not attempt to get anyone involved in bitcoin (and to adopt bitcoin) that could potentially get involved.
The ability to say something potentially controversial without associating your "main" forum identity/reputation with such message. For example if someone decided one day that they thought they found a reason why Bitcoin is going to fail but they are not 100% sure if they are correct, they may wish to purchase an account in order to force the discussion of this potential flaw without risking the embarrassment that would follow if they were wrong. Granted someone could just create a new account to do this however people tend to not take brand new accounts that make these kinds of statements very seriously - they are often almost automatically written off as trolling. There are other numerous examples of what could be said with purchased accounts. This is a pillar of freedom of speech. To truly have free speech, you not only need to be able to speak what is on your mind but also be able to do so without your identity being revealed
I can say something without revealing my identity. I just need to create a new account. Using other people's account, however, is not just not revealing my identity, but rather replacing somebody. And using the new account's activity and reputation is deceiving to say the least.
I'm sorry, but I don't see this point as legitimate.
I also already countered this point. If someone were to create their own account to say something controversial (and the account is brand new) then whatever they are saying will be 100% not be taken seriously and will be assumed to be trolling (almost all the time). On the other hand if someone were to purchase a more established account then posting something controversial is more likely to at least be looked into.
For avatars. This is somewhat less common, especially as the percentage of overall accounts available with avatars is rapidly decreasing, as well as the fact that the new forum will likely have avatars.
This is circumstantial.
I can say for a fact that accounts with avatars have greater demand. You can almost always charge premium for an account with an avatar
To get around the 360 second posting rule and other newbie restrictions
The newbie restrictions are there for a reason. This is not a legitimate reason to buy an account.
The reason there are newbie restrictions is to prevent people from spamming and scamming with throwaway accounts. If you create a new account and get banned/negative trust for spamming/scamming then you can simply create another account with essentially zero effort. On the other hand if you were to invest the money to buy an account to get around the newbie restrictions then you have an incentive to follow the rules and not to scam because if you do then your 'investment' will have gone to waste because your account will either be banned of have negative trust.
To have the prestige of having a higher ranking account. Some may think this is somewhat dishonest and may be against this however it is a source of demand for accounts.
I'm not sure if something can be both dishonest and legitimate, but if it can, then there's a problem with our society.
I am acknowledging that some may
feel that this is dishonest however having the prestige of a higher ranking account is not going to give them any kind of advantage, it is only going to stroke their ego.