The "I don't have enough time to grind" and "I don't have enough time to farm" arguments are typical of people advocating powerleveling and buying gold, from the posts I've seen. It's a weak argument. I can say this because I am 34, married, with a full-time job which requires me to be on call until 9:00pm every weekday, and a hefty mortgage which means I can't take unnecessary days off to play, and yet in the three years I've been playing I've leveled three characters to 70, bought epic flying skill on two of them, taken them through quests all through Azeroth and Outland, managed to get in numerous heroic instances (usually only on Friday evenings or weekends so that Mrs. Wondy doesn't feel neglected), and even done a few Kara runs, ZA runs and a miserably failed Hyjal run. If I were single, paying less in rent, and could win the lottery, I'd probably be much more hardcore, and devote a lot more time to gaming, instances and raids.
If you're casual, accept that you're casual. I know that sometimes you see people in the big raiding guilds and think "Wow, I'd love to get some of that gear". But there's a difference between having in-game goals and aspirations and thinking "Wow, I wish I could just buy that gear on eBay". The problem I see with that is that by letting someone else level a character to cap, or by buying a character that someone else has already leveled and geared up, or even buying gear or gold is that, in the end, you don't really appreciate the accomplishment that it's supposed to represent in the game.
To use a real-life example, when you were a child and your parents bought you a toy, you didn't worry so much about it if it broke- because it wasn't your money that bought it. However, when you saved your money and bought an action figure with it, that was your investment, so it's more precious to you. As an in-game example, take the Amani bears. In the beginning, they represented an accomplishment- they were only available to people who could successfully complete the bear run in ZA within the time limit. However, as major raiding guilds started to farm the run, they started selling spots for people to get the bear. Now when I see the bear, unless it's someone that I know got it before the spots went on sale, I assume it's someone who had 8,000 or 10,000 gold. In my opinion, that cheapens the accomplishment of those that got it the hard way.
Everyone has the same time in a day. Everyone also has choices which they make on how they use that time- sleep, study, work, or play. Most people with traditional jobs work a 7- or 8-hour day. Most people that go to school have to devote at least the same amount if they want to make decent grades. People who don't work or study (whether they are unemployed, on medical leave or other reasons) don't have that 8-hour commitment every day. That's their choice- just as the student chose to get an education and the working man (or woman) chose to get a job and make money. It takes away from your free time, but it's your choice.
Whether you choose to spend your free time gaming, raiding, or following other commitments is immaterial. When real money gets introduced into the game, people that make more money have a distinct advantage. If player A is on a disability pension, he may be playing more hours than player B, who makes $50,000 a year, which means he would be able to do more in the game. However, when player B buys a level 80 warrior which is decked out in heroic gear, he's just leaped past player A. This, to me, cheapens the achievements of player A (and anyone who plays for longer or more hardcore). Player B doesn't want to put in the time and effort needed to earn the character, but a quick drop of $200 gets him something that player A cannot afford, in a few seconds. Think of it this way. Player B just bought his character and joins a group. In it are player A, player C, Player D and player E. Player C makes over $100,000 a year, and also bought his restao shaman a couple of days ago. Player D makes $65,000 and has a legit copy of the game, but got his druid power leveled from 65 to 80, because he got tired of the grind. Player E makes $55,000 a year, and he leveled his character from scratch to level 80. They go into a heroic and wipe. In this case, regardless of how much people made, it's the people that bought their accounts that made the run suck for the two that didn't. It doesn't matter how much you can throw at the game- it matters how your actions, abilities and skill affect other players. If you buy a toon and solo, so be it. But the moment you come into a group with suckasstic skills because you haven't learned your class' basic mechanics, you suck.
And that, my friends, is my opinion on why arguments for gold buying and power leveling are for weak-minded feebs who like being spoonfed.