The myths are:
Military recruits are less educated and have fewer work alternatives than other young Americans.
The military tends to attract people with lower aptitudes.
The military attracts a disproportionate number of poor or underprivileged youth.
A disproportionate number of recruits come from urban areas.
The military isn’t geographically representative of America.

All Things Conservative has a description of the 5 myths of military recruiting and their responses. The original article on blackanthem.com is somewhat longer.