The EQ2 wiki entry has an important factor that many CoH players seem to overlook when citing Everquest as proof that changing sides can work:
You may also be forced to change your character class in the process. Whether you change class or not, your spells and abilities are permanently reset.There in lies the major problem in switching between sides in City of Heroes. The sides are not the same. All classes are inherently different, and one of the strengths of CoH is that each class is supposed to give a completely different play experience. A brute should not play a tank. A stalker should not play a scrapper. A Corruptor should not play like a Defender. A dominator should not play like a blaster. A Mastermind should not play like a Controller. I've been over this concept and the differences between archtypes multiple times.
Yes, in one case a villain class does share some of the exact same powersets at the exact same levels as a hero class. The Brute Archtype does have the same exact melee and defensive levels as a scrapper. However, the Brute has a higher hitpoint capacity than a scrapper, access to several armors scrappers don't have, and weapons scrappers don't have. Scrappers as well have an armor set Brutes don't get.
- Scrapper Armor: dark, fire, invuln, regen, shield, super reflexes, willpower
- Brute Armor: dark, electric, energy, fire, invuln, shield, stone, super reflexes, willpower
- Scrapper Attacks: broad sword, claws, dual blades, dark, fire, katana, martial arts, spines
- Brute Attacks: battle axe, dark, dual blades, electric, energy, fire, stone, super strength, war mace.
When something like this pointed out, the person requesting ability says something to the effect of "no no no, I mean I want to be a brute, but be a heroic brute." In other words, they want to take an archtype from one side of the game, and have that exact same archtype on the other side of the game.
People who want something like this don't understand City of Heroes, or the concepts behind the game. The point of a game like City of Heroes is that each side is unique, and offers a different play experience. There are some powers that you can only get on Villain Side, and there are some powers that you can only get on Heroside. Yes, the developers could make a Hero version of the MasterMind, but that would make the MasterMind archtype less unique, and less special. One of the key design goals, and one that even Jack Emmert couldn't ruin, is the uniqueness to each powerset, and to each player.
While I'm not going to argue that some playing styles and enhancements sets are best suited for specific avatars, there are a wide range of powers one can go through. A good case in point is my stalker. Many of the Ninja Blade attacks offer a defense debuff and can slot defense debuff and accurate defense debuff IO's. I can focus on pure melee damage, or I can combine a strong melee damage boost with a 10% chance to-hit proc boost and work on a high regeneration boost with the debuff sets, or I could get an average 2% boost per power to base damage with the defense debuff sets coupled with a strong boost to melee damage and accuracy.
Allowing players to magically port, transfer, betray, or whatever one side for another and keep the exact same archtype with the exact same powers would kill the uniqueness of the game, and I honestly don't think the current development team is that dumb.
Now, there are other specific reasons which make sense to me as a long-term player. I see the inherent values in how tasks in the game are balanced for each side. I went over some of these factors in the creation of what I call the Mongoose Strike Force. The Positron Task Force on the side of the heroes was built with the idea of having a mixed team that could cover each other's weaknesses. The lack of answer to the Defender archtype means a direct answer for Positron just isn't in the cards for the Villain players. A Villain positron can't have as many status effects or mezzing enemies, simply because the Villains can't counter those effects.
At high levels the differences are more pronounced. The Statesman's Task Force depends on a strong tank to hold Lord Recluse and the Final AV's in Place. Like or not, the average tank simply isn't going to be capable of standing up to Lord Recluse and Company, and even a Stone tank who has granite armor isn't in position for an automatic win.
In a similar manner, the LRSF is designed so that not just any Brute can handle Statesman. A Tank versus Statesman? Well, even my worst tank can easily handle Tyrant conning as an Archvillain on an 8 man invincible praetorian arc. Little reason to think then that my worst tank would have a problem if it could run LRSF.
For villains, having a true tank would ruin the challenge of many of their strike forces, and Heroes, having a scrapper with a higher health bar poses similar problems.
These differences are sometimes very pronounced when fighting in the mixed Task Forces such as Lady Grey and Imperious Task Force. The task force has to be balanced so that they can be completed if Tankless, or with weak debuffs. Some can argue that LGTF is hard to complete without strong buffs or debuffs, citing the over-powered WarRiders, and I'd have a hard time disagreeing. However, many of these challenges depend on a larger available selection of archtypes, rather than a limited selection of available archtypes, to make the challenges work.
It's a subtle difference, and it's why many suggestions made on the CoH forums are simply passed over. Designing for an MMO like CoH while keeping the strengths and weakenesses on each side in mind, and developing for and against those strengths and weaknesses is a challenge.
There are very good reasons why Martial Arts will never be a Blaster Secondary, and why there will never be a Hero version of the Mastermind.
Some people just seem to be incapable of understanding what those reasons are. The biggest worry is that the developers might lose sight of the design goals of the game. That has happened before to at least one NCSoft game, which was Tabula Rasa, and the result is the game going into it's final hours this month.
If the development team decides that players can turn from one side to the other, that event would mark the exodus of a large portion of the CoH player base... and again, I don't think the current dev team is that stupid.