Look at it from a business standpoint....
If you allow this, more players will want to return to WoW or more copies and subscriptions of the game will be sold. Blizzard makes more money, the WoW population increases, more people are riding that horrible Obsidian Nightwing, and there are more people to populate LFG/LFR. Maybe the queue times won't be 30 minutes for a DPS class because more Monks will be tanks or healers... everyone gains from this.
I think it is a smart move on Blizzard's end do to this. Also, instead of complaining about it costing money to do it, why don't you get a job (or another job), save your money, ask your parents for money to get another account to do RAF.
Or you could ACTUALLY recruit a friend to play.
wait, that wouldn't make sense. Too much effort to have something handed to you.
It's not about the cost, it's about buying an advantage for the realm first monk achievement. They can allow monks in RaF, just disable the achievement for the ones that skipped to 80.
Well, I think that if you are going to spend a few days in a row not sleeping or eating or being somewhat healthy because you are pushing for a Realm First achievement, then I think buying your way to 80 is completely acceptable. If you have to buy your way to a realm first by giving up sleep and exercise and a life outside of WoW, then there are bigger fish to fry.
I'll gladly take 8 hours of sleep over a Realm First achievement any day. Let Blizzard make their money. You will continue paying to play and paying for expansions until you move on from the game. I don't think allowing RAF to work for Monks is going to kill the business or make people quit playing. In fact, I think quite the opposite. They should generate more revenue from this release than WotLK because of the RAF for Monks.
Really though, rather than complaining about how the system doesn't work for you, why not try making the system work for you? You have over 1 month to save up the money to purchase another account. If you think it is valiant and chivalrous not to buy your way to 80, then don't. But don't complain about an achievement that you probably wouldn't get anyway.
Like the old saying goes... if you can't beat 'em, join 'em.