+1
LOL, those kinda' folks are ignorant^N
As someone who has personally assembled several home-made machines using good cases and parts, you are glossing over some of the pitfalls with the home-built approach:
1) Components (esp. cases) almost always look better online than they are in reality.
2) Even sturdy parts have quality issues like vibrations, poor tolerances (things don't fit exactly right), cable routing issues, sound...
3) The fun of getting everything installed (drivers, etc.) to work properly out of the box can be a matter of minutes, hours, or days depending on which components you happen to pick
4) Cut hands due to very sharp internal edges (minor annoyance)
5) Supporting failed parts... RMA'ing, replacing and following up with manufacturers individually to get a working machine
But hey, once you get through all of that, the dollar cost is usually significantly lower and there is a sense of accomplishment. But, let's not pretend it's for everyone.