Why not buy new? $1800-2000 buys a nice bike. You get exactly what fits you, you get warranty coverage, and you typically get free tuneups. And everything works crisply.

Conversely, a two year old bike, assuming its been ridden a fair amount is going to be showing some wear. To get it to perform close to new, you're likely looking at a new chain and cassette. You'll also likely spend money for a new stem to get the bike to fit you, and you'l likely buy a new seat to meet your preference (something that can be swapped out on a new bike at little to no cost usually).
Also you may be looking at new tires and brake pads. So not unreasonable to add $200 or more to the cost of the used bike, as fitting/refurbishing costs.

As an example a new Canondale Supersix 5 (with 105 components) has an MRSP of $2399, and our local dealer has a 20% off sale right now. So you could have a brand new Cdale, with warranty, fitted to you, for less than you'd likely end up spending in total for the Argon.

IMHO, used bikes make a lot of sense with a budget under $750-1000 because it's hard to get a new bike without significant compromises. With a budget of $1500 or more you can get a very nice new bike, and it becomes more questionable to go used, just to get a slightly higher line bike.