- Change Human to : 1 extra feat, 1 extra skill, 1 extra weapon proficiency
An extra feat would be way too much. It would allow them to duplicate a key perk of many other races, and often exceed them. Wood elves, for example, are often picked for that +5 to movement speed. Well, now humans can start with +10... with added movement related benefits. That +1 hp per level that one dwarf race gets? Yeah, humans can now start with +2. And just that it would mean that humans can start with a 19 in their main stat... The only way to balance such a thing would be to give the humans a serious disadvantage, like giving up the +2 to a stat, or else the +1 to a stat and having a limited selection of feats they can choose.
Note that alt humans, the reason why people bring up the "give humans an extra feat" idea, do just that... they give up stats to get that feat. This allows for human flexibility, while still letting the other races have their specialties.
I could see giving humans a second +1 to a stat, which is essentially a half-feat. This means they could start with a 17 and two 16s, so it is quite a strong perk, but it wouldn't allow starting with a 19.