There is a common theme, across various different mythologies: that of the dangerous goddess.
The dangerous goddess appears across many different cultures, in many time periods and in many forms. In the myhtology of the ancient Levant, Anat wades in the blood of her enemies and severs the limbs and heads of the fallen; in the legends of Ireland, the Morrigan rides shrieking into battle to destroy her foes and hangs their bodies as omens of deaths yet to come; in the vibrant mythology of India, the great and terrible Kali drinks the blood of the evil and the dead and dances destructively, drunk on her own power; and in the long-ago stories of fallen Babylon, Ishtar threatens to tear the gates between the very worlds apart and the gods tremble before her fury. Egyptian Sekhmet rampages across the world so that humanity is in mortal peril of being wiped from the face of the planet, while Arctic Sedna drags impious sailors to their doom with long, grasping tendrils of hair and Phrygian Cybele causes a frenzy in her worshipers so wild that they castrate themselves and die still speaking her name.
These are not the only dangerous goddesses in mythology around the world, but they make an impressive row of terrors even without their wild-eyed sisters. Clearly, the ancient idea of the deadly and uncontrollable female is widespread, and those who tell their tales are both terrified of their unfettered power and worshipful of their awe-inspiring abilities.
In general, Power with a capital P is the reason for these goddess' existence. They represent awesome energies, and more importantly, they represent quintessentially female energies, which make them uncommon and frightening even among the ranks of the gods. For many ancient cultures, feminine power was considered fundamentally different from masculine; it was undeniably important but confusingly mysterious, effective at routing the enemy but prone to turning on friends, undeniably necessary to the universe but sometimes a force for evil in it as well. The concept of the power of the goddess being fundamentally different from that of a male god is deeply entrenched - not only in the myths of those cultures who believed it millennia ago, but also in our modern scholarship and study on the subject, which carries the bias and perspective of century upon century of cultural assumptions no matter who tries to talk about it or what their goal might be.
But regardless of why the dangerous goddesses are treated differently, they all have one thing in common: everyone is completely terrified of them.
There is a lot of psychological study into why a goddess of terrible raw power is so much more frightening in many ancient religions than a correspondingly dangerous male god. Why should everyone be so much more afraid of Cybele than Dionysus, when their rites were often almost identical and their focus on religious ecstasy bordering on madness the same? When Shiva is the most dangerous being in existence, capable of wiping everything out should he so choose, why is it Kali who more often strikes fear into the hearts of listeners and tale-tellers alike? In many myths, it is precisely because the goddess is female that she is so terrifying; from a sociological point of view, ancient patriarchal cultures viewed females as people who needed to be controlled and who formed the necessary backbone of society. Women were wives and mothers, the foundation of labor in homes and cities and the vessels through which family lines and household affairs were conducted and preserved. For a woman to go rogue meant that she became a dangerous and unknown quantity - simply her absence might cause a massive upset in an ancient Norse household, where she would be in charge of the running of the home and the finances of the family, or her political support of a rival family might spell doom for a Roman senator who learned too late that she was not on his side. And in cultures that hung their definitions of masculinity on the role of a man on his ability to defend his home and family against outside threats, a woman who did so on her own told society at large that men were unnecessary, threatening the social construct by which their lives were governed.
Of course, in some cultures, none of this applies. Some ancient cultures were matriarchal, and had no need to consider a female deity dangerous just because she was female; and in these myths, you more often see powerful goddesses who are not uncontrollable monsters but rather potent and influential in their own right, like Amaterasu regally ruling the courts of Japan's heavens or Na'ashjéii Asdzáá weaving the world upon her cosmic loom as a creator and teacher. Some cultures don't view deities' genders as solidly and unchangingly, so that warlike Oduduwa might appear as female with no change from the way the god was represented as male, since both are equally applicable in different areas of Yoruba myth and one does not carry more or less weight than the other. Some cultures are capable of containing both, and late-era Greek worship saw Cybele's frightening cult rubbing elbows with temples to wise Athena or queenly Hera.
But for those cultures that do draw a line, the dangerous goddess always represents the dire consequences of the uncontrolled female: a being that can and will ignore social rules and traditional laws, whose power cannot be bound by convention and whose desires and motivations may be unfathomable to others. Some cultures, like the Norse, assigned femininity to powers they did not understand or condone, like witchcraft, and therefore attached the stigma of forbidden and dangerous power to anyone who might use it; others, like the Mexica, claimed physical power as the domain of men only, and called women who dared aspire to it unnatural and unacceptable. In all that present the dangerous goddess, she is in some way too much of a threat to be left alone, and must be reined in in some way. Often this is through assigning her a "keeper", someone who must temper her power with reason: Ptah must balance Sekhmet, Shiva must keep Kali in check, and Ishtar must be married off to Tammuz to calm her youthful wildness.
Dangerous goddesses may have represented the old ideas of woman as irrational and threatening if not controlled, but in the here and now, it is not hard to see that their roles have changed and are still changing, especially for those who are still worshiped today. They are not just weapons to be wielded by the male gods; they are forces unto themselves, representing many things and fulfilling many mythic roles. They are lovers, soldiers, heroes and villains no more or less than any other deity, and those who forget that they are more than a sword or a set of teeth do so at their own peril.
So walk with respect before the dangerous goddesses, the Durgas and Coatlicues, the Ereshkigals and Morenas. They're more than just a bloody face.