Long-range hunting is no more unethical than shooting a running deer in the bush at 50 yards. It ALL depends on the skill of the shooter.
Some of the early posts in this thread make me laugh.
Here is how you can gauge whether or not you're ready to shoot at game at any given distance:
Bundle up in your hunting clothing. Put on your pack and hunting gear. Set up your targets along the towerline you're talking about. Walk along at random distances to the target. Get into your field shooting position, range the target, read the wind, dial in your corrections, take the shot. Come back tomorrow and do it again. When you can connect on a 10" circle 9 times out of 10 on the first shot of the day, then you are ready to shoot at a game animal at that range.
You will quickly learn that you will have to pass on some shots because of the circumstances. It doesn't all have to do with range, either. I would greedily take a shot at 600 yards at a broadside animal, standing still, with no wind and a clear shot from prone, over a 300 yards shot at a quartering animal in a brisk 25mph gusting cross wind.
You will certainly need a GOOD range finder like a Leica, Zeiss, or Swarovski if you plan on shooting much beyond 400-500 yards in the field. You'll need plenty of practice to determine elevation and wind corrections in various different conditions, and then make yourself a drop chart and tape it to your stock. You'll need the right optics- something clear, repeatable, and tough. You'll need an accurate rifle that is capable of sub-MOA accuracy. You'll need good bullets, and keep in mind that cartridges and headstamps make ZERO difference. What matters is that you have a good bullet and enough velocity to expand that bullet at range. Then you need a LOT of practice.
I would suggest something like a Savage or Tikka in 7-08, .280, or 7RM with the 162gr A-Max or 168gr Berger VLD, or something in .308" (.308W, .30-06, .300WSM, etc) with the 155gr Lapua Scenar. Others will work, but any of these would be good choices.
As far as scopes go, many will work, but you need the adjustments to be precise, repeatable, and rock-solid, above all.