Going to keep this simple as I have paid attention to what has been said by those who would know, and my understanding of security procedures with online games.
At this point in time, the launcher re-downloads the base required files for the game each time you log in as a preventative measure to hacking those files. By re-installing those files each time the game is started, it counters any hacked versions of those files and negates people attempting to cheat that way. So at this time, if you want to play, you have to allow this to happen each and every time you start the game client. If you don't want to deal with the anti-hacking measures, then don't play.
As [GM]Ebilfish stated, they are looking at changing it. So based on his statement, in the future they are hoping to have those files only checked for changes instead. Then it would only re-download them if it does not pass the file verification and after re-installing the file or files would then proceed to start the game as normal. Regardless, it is all just a security measure to help prevent hacking and people cheating the game and ruining it for others.
So in short, the game is just doing a basic security measure and it should not even be a concern. Let it do what it needs and enjoy the game.
WhiteHeart.WU1 of the Wu forces - AKA - White Dragon
Weapon - Boomerang
Rank - Field General
Current Guild - MoonWalk
Guild Rank - Officer