Interesting article, though probably wrong at least in some places (pdf):
Conventional wisdom has regarded low self-esteem as an important cause of violence, but the opposite view is theoretically viable. An interdisciplinary review of evidence about aggression, crime, and violence contradicted the view that low self-esteem is an important cause. Instead, violence appears to be most commonly a result of threatened egotism—that is, highly favorable views of self that are disputed by some person or circumstance. Inflated, unstable, or tentative beliefs in the self's superiority may be most prone to encountering threats and hence to causing violence. The mediating process may involve directing anger outward as a way of avoiding a downward revision of the self-concept. [. . .]
Comparing self-esteem across racial or ethnic groups is complicated by several factors, such as measurement issues and temporal changes, but the very possibility of temporal shifts presents an appealing chance to look for covariation in self-esteem and violence levels. In the 19th and early 20th centuries, American White men presumably were fairly securely convinced of their superior status. This confidence is generally assumed to have eroded in recent decades, and indeed research now indicates that Black people have self-esteem levels equal to or higher than those of White people (see Crocker & Major, 1989, for review). Concerted efforts to boost racial pride and dignity among Black Americans in the 1960s and 1970s may have contributed to this shift.
Meanwhile, violence levels also appear to have changed, and these changes directly contradict the view that low self-esteem promotes violence. During the period when White men had the highest self-esteem, they were also apparently the most violent group. Historians believe that rapes of White women by Black men were quite rare, whereas the reverse was relatively common (e.g., Brownmiller, 1975). Likewise, the majority of interracial murders involved White men killing Blacks, a pattern that is still reasonably well documented into the 1920s (e.g., Brearly, 1932; Hoffman, 1925; Von Hentig, 1948). These patterns have been reversed in recent decades as Black self-esteem has risen relative to White self-esteem. According to Scully (1990), Black men now rape White women approximately 10 times as often as White men rape Black women. The timing of this reversal appears to coincide with the concerted cultural efforts to boost self-esteem among Blacks: LaFree's (1976) review of multiple studies of interracial rape concluded that researchers found approximately equal numbers of Black-on-White and White-on-Black rape in the 1950s, but since 1960 all studies have found a preponderance of Black-on-White rape (see also Brownmiller, 1975). Similarly, recent murder statistics indicate that the strong majority (80%–90%) of interracial murders now consist of Blacks murdering Whites (Adler, 1994). Clearly, both races have committed far too many horrible crimes, and neither race can find much claim to any moral high ground in these statistics, but the shifting patterns on both sides repeatedly link higher or rising esteem with increasing criminal violence toward the other.
[Baumeister RF, Smart L, Boden JM. Relation of threatened egotism to violence and aggression: the dark side of high self-esteem. Psychol Rev. 1996 Jan;103(1):5-33.]