A surprising number of players on these forums seem to love the idea of spending $2 a month for extra retainers with justifications spanning the entire spectrum. I'm going to my best to refute every one I've found so far, so please read this entire post before you find one point you want to nit pick.
1. First, and most importantly in my opinion, is that retainers are not just extra storage space anymore. If these retainers can only do exactly what retainers can do before 2.2 then I don't have as much of an issue here. But once 2.2 launches retainers will turn into something more than just extra storage and market slots, they'll be able to go on ventures. These ventures can gather unique items exclusive to retainers so presumably someone with more retainers has a higher chance of getting these items. I would consider that an advantage for players that decide to pay extra money.
Now the counterpoint to this would if you only allowed two retainers to go out on ventures at one time. This would basically put everyone on even grounds regardless of whether they bought extra retainers or not. Some people argue that because these ventures need "venture tokens" players wouldn't be able to afford to send more than 2 out anyway, but these tokens can be bought for GC seals, 5 tokens for 1,000 seals, so running out of tokens is not a major hurdle.
2. Another point a lot of players make is that in FFXI people paid extra all the time for the storage space in the form of mules. I would argue that was because the subscription model was set up with that in mind. Here the "Standard" subscription includes 8 characters which is plenty of storage and includes 16 retainers in total (once you unlock them for every character). But there is no easy way to transfer these items between characters without some middleman or FC chest. We're basically being asked to pay a $2 monthly convenience fee to save us from having to transfer items back and fourth between our characters.
What I would rather they do is give me the option to trade some of my extra character slots that I will never use into retainers on my other characters. SE will save having to store character data for characters that are never played in exchange for retainers that will actually benefit the players.
3. It's paying real money for an additional storage space and could easily lead developers to introduce more and more items players will want to store. Whether it's using new items for future crafting recipes instead of using existing ones or adding 12 new pieces of headgear with each event that can't be stored in the armoire.
4. The server cost of additional retainers justifies the $2 monthly fee. This argument is the worst in my opinion. As I said above for $15 you can get 16 retainers, in addition to the character data for 8 characters. So how a retainer can justify a $2 monthly fee on it's own is impressive.
You have to remember that the most expensive thing (server wise) that a player does in any MMO is to actually log in and play the game. If you can justify SE charging $2 a month for a retainer to compensate for their server costs then what next? Do you think someone that plays 5 hours a day should pay more than someone who can only get on for 2? I don't want this game to turn into my phone companies data plan, with different pricing tiers depending on how much data I use a month.
For anyone who actually made it through that wall of text I thank you and hope we can have a civilized discussion in regards to the points I made here.