The problem here (and in the other billion threads on this subject) is that Sins, thank Heavens, doesn't fit neatly into a "box". It's not really an RTS, and it's not really a 4X game, and that makes a number of people very uncomfortable. Some people seem to like boxes. Now that the community has Sins in their hands, the hardcore RTS fans are trying to push it more into being an "in the box" RTS, and the 4X fans are pushing the other way. (1)
The people (such as the devs) who understand that a game doesn't have to fit neatly into one of these arbitrary, boring "boxes", seem to be a minority, and so it's hard to find a peaceful resolution to this problem. (2)
The more the game moves toward what will make one group happy, the more it moves away from the other. (3)
Competitive play doesn't have the same requirements as casual play, and has very little in common with single-player play. (4)
This shouldn't be surprising to anyone that gets outside, much. (5)
Your weekend baseball, tennis, parking lot basketball, chess, or poker games don't use hardcore tournament rules, because that'd be stupid, and actually lessen the fun for everyone involved. (6)
Hardcore, competitive RTSs are played in a completely different fashion than normal matches, and have different needs and requirements. (7)
Thinking otherwise just means you don't understand how to play the other way. (8)
(1) Nice strawman. The 'hardcore RTS players' are not your enemy, and there is not some kind of 'battle' going on between competitive and casual players. Competitive players spend many hours getting to know the guts of the game and can see things that are imbalanced. They are making a case to get these things changed.
(2) Whether the game fits into a 'box' or not is a totally pointless completely subjective discussion. What we're talking about here is game balance. Since this game has soooo little micro method, almost all of the game balance discussion can be demonstrated with simple math (and there are several good threads where this is going on right now). So it's as objective as it can possibly be.
(3) This seems to be an ongoing theme in the 'everyone hate the competitive players' crowd. All the competitive players want is game balance. Your point might be relevant if there were two games being developed, and the devs would only work on one at a time. But this is not the case. If you can play TEC and spam trade ports by exploiting the new low-cost/low-risk black market in multiplayer, you can do it just the same in single player. The presence or absence of AI has nothing to do with whether or not TEC trade spam is too powerful a strategy or not.
(4) This isn't true. Maybe if this game were Starcraft or something where advanced micro methods made some units much more powerful than using them the naive way, but there is nothing like that in this game at all. All the balance in this game has to do with 1 of 2 things: either the order of the tech tree or math. Anyone that owns this game has the SAME ability to go into multiplayer AND single player. There are no extra 'requirements.'
(5) Insulting people will get us nowhere. It will get nothing accomplished. Insinuating that 1) competitive players are all weird nerdy types that live in their basement and 2) that this is somehow a bad thing are uncalled for.
(6) I like your analogy, so I'm going to use it myself. You are probably correct in that a lot of casual players of other games don't use 'hardcore tournament rules.' For example, two tennis players may decide to play a game without using the out-of-bounds boundaries. There's nothing wrong with this, and I don't think you'll see any competitive tennis players decrying them for trying to destroy the game. However, these two players are not playing tennis. They have made up their own rules for their own game.
Similarly, players that simply choose not to use overpowered strategies or that choose to 'ban' them from gentlemen's games are not playing Sins of A Solar Empire. They've changed the rules of the game to their needs. It's just as if they had made a mod that did away with the possibility of using overpowered strategies - it's not the same rule set, so it's a different game altogether.
However, this doesn't mean that they don't use any rules at all. If my friends and I are playing poker together, it isn't fair if the specific rules we're playing by say that Don wins if he ties with someone else. That's unfair and tilted towards Don. Most people realize that unfairness is a bad thing. I won't go into this since it's basically a huge philosophical argument.
(7) In games like Starcraft, competitive matches ARE normal matches. In this game, there are just too many options to define what a normal match would be. Is it slow research? Fast build, fast movement? 1v1 or 3v3? What is a 'normal' match?
Besides those questions, what difference does it make? There isn't an option in the game to 'Balance Black Market so It's Not Skewed Towards TEC' so your point is moot. If something is overpowered, it is overpowered regardless of the setting or the situation or even occurences. Even if you lose miserably using something overpowered, that doesn't make it any less so.
(8) Declaring yourself correct isn't the best way to proceed in an argument

. I would respond to this by saying that thinking the game is balanced just means you don't understand how to play the game competitively.