By 'careful' I meant carefully type in the codes or download them. Get the codes from good sites - there are ways to easily evaluate whether a site is valid or not. Using an AR or other cheating device - I know you're taking a risk.
As for how I hack...
1. I don't hack until I've beaten the Elite Four at least twice, and tried to capture every legendary on the game, and tried to hatch shiny Pokemon or search GTS.
2. I love legendaries and shinys. (But don't we all?)
3. I, for one, don't cheat that often, and often times I give hacked Pokemon away to those who want them.
So, that's my argument, but it may only apply to me and a few others. (Plus, I would never use hacked Pokemon in an official championship.)