Why are so many people against Arena in Swtor?

Because trading kills for fast valor and gear doesn't happen in arenas.

They're just bad and if arenas hit, everyone would see how bad they really are without a dozen people carrying them.
Don't pvp at all? Then why do you even care? Don't participate. No one here is going to force you.

Don't know bout anyone else, but my friends and I are totally waiting for arenas to hit.

Keep waiting. The developer's love your money.

Arena didnt really have much skills on WoW either, it was about gear and what classes you played, we real pvpers want world pvp.

Yeah, right. I love world PvP, but it's an utterly non-competitive environment. I'd prefer ranked WZs. Besides, this engine can't HANDLE world PvP on any fun scale. I've got a PC that's only obsolete if you love hardware, and get a slideshow at around 75 people trying to kill each other, with bad performance at 45-50 or so.

And trust me, you don't want to get the "Let me play MMOs on a pocket calculator" crowd in here...

MMOs should not be balanced for small scale fights, like arenas. There would be a couple of classes that would own in the arena, then the other classes will cry and the devs will have to try to balance the game specifically for arenas. When that happens, any PvP with more people will be completely ruined aswell as PvE. Blizzard said it was the worse thing they did to WoW because of balance.

Ding. Not to mention it adds a THIRD gear grind to a TWO Gear grinds sort of game.

You answered the question yourself - class balance. "Very similar" classes doesn't mean "the same classes" and there will never be such perfect class balance where some classes are not hard counter to other and they have a hard counter on them. Arenas promote FotM builds. For example - get an operative vs sage 1 on 1. Fine, operative is a counter to a squishy. But that doesn't mean that the sage will lose every single time 1 on 1. Few times he will win. But... what happens when you gather 4 of the current FotM classes and put them in the same team? Faceroll... until they get nerfed and rendered useless. Then the next FotM... then the next... and the next. And it will never be balanced. I stopped playing WoW long ago (few months after WotLK) so i don't know the situation now. Back then the 2v2 brackets were completely dominated and destroyed by unholy DK/holy pala combo. Utterly destroyed. What about the 3v3? How long, for how many years the RPM were obliterating everything and completely dominating the 3v3 brackets?

That's the problem with Arena based PvP - they always promote the FotM classes, no skill involved, it's only the best possible combo facerolling the others.

Don't get me wrong, i'm two thumbs up for rated PvP. But as it is now - rated warzones with objectives. That's a compeltely different scenario. Trying to outsmart the other team, capture the objective and keep it, beat them with tactics and not with OP classes (e.g. 4 operatives pop out of stealth on one sage - hai!bai! - omg, we so pro! ). Arenas will just force them to start "balancing" the classes thus "fixing" the OP classes, usually breaking them, and making some other class to be a complete faceroll so the new FotM combo becomes available on the next patch... There's simply no need for arenas. Just rated warzones and full premades, that's it.

Here's what I'd like to know. Why are so many people determined to have a formal Arena system built into the game? There's an area for PvP between groups. If you really want Arena, organize it yourself.

Arena PvP is fun, but it puts class balance under the microscope.

While a lot of imbalances are hard to identify and fly under the radar is larger scale PvP, adding Arenas puts a lot of preasure on developers to give every class a fighting chance.

These balance changes inadvertently affect PvE at some point which in return drives PvEers up the wall.

You can end up with weird situations where a class is the best healer in PvP while being the worst in PvE (Shamans in WoW). How do you balance that?