Instead of seeing the Ten Commandments as mere human creations that reflect a particular religious culture from a specific historical time period, some people regard them as fundamental moral rules that God laid down for all humans to follow. In his Confessions (Book III, Section 8), Augustine presents them as divine proclamations of our duties to God and to people, while people today appear to be doing the same thing when they erect monuments with these commandments etched into them.
Upon close inspection, however, one finds that there's a surprising amount of really important stuff missing that one would expect fundamental moral rules not to leave out. Because of these omissions, then, the Ten Commandments can't provide an adequate list of such rules. Here are just five examples of what's missing:
1. Commands outlining how to treat children well.
The Ten Commandments command people to honor their parents (even if they don't deserve it? what does it even mean to "honor" one's parents in the first place?). However, they don't do a very good job of outlining how to treat children well. They appear to forbid murdering children, stealing from them, and bearing false witness against them (if only implicitly), yet there's nothing about obligations not to harm them in non-lethal ways or about the need for people generally to be nice, nurturing, and respectful to them. There's nothing about the duties of parents to meet the needs of their children or to do any of the other things that parents should do for their children. Children comprise a rather large and very important part of the human population, are especially vulnerable, and have distinct and extensive needs, so an adequate list of fundamental moral rules should contain at least some explicit directions for how to treat them well.
2. A condemnation of slavery and human trafficking.
The Ten Commandments condemn murder, theft, adultery, and bearing false witness against others. But one of the most striking things about them is that they fail to condemn the morally horrific practices of slavery and human trafficking. Like murder, these things involve a severe moral failure to respect the fundamental rights that people have to direct their own lives, and so they are severe moral wrongs that an adequate list of fundamental moral rules must condemn.
3. A condemnation of sexism and racism (along with any other morally objectionable "-ism").
The Ten Commandments are completely silent when it comes to sexism and racism, and yet it is of great moral importance that people not be mistreated, or seen as inferior, on account of things such as race or sex. Sadly, both history and our world today are rife with racism and sexism, and some of the most brutal mistreatment of others is racist or sexist in nature (just think of American slavery or the horrific treatment of Islamic women in the name of Islam). Given how disrespectful racism and sexism is generally, how brutal these ridiculous things can sometimes be, how many people they can negatively affect, and how prone to racism and sexism humans have generally been, it is evident that an adequate list of fundamental moral rules should condemn them.
4. A command to be charitable and fight poverty.
The Ten Commandments command people not to covet the things of others, but they don't command people to be charitable and fight poverty. Though it might be unclear how charitable we need to be, or how much we should give up to fight poverty, we all should be charitable and fight poverty to some degree. In light of the extent of need and poverty around the world along with the general human tendency to do nothing about it, an adequate list of fundamental moral rules should instruct people to combat as much poverty and need as they can within reasonable limits.
5. A command to treat sentient non-human animals humanely.
Whether or not sentient non-human animals have rights, they are still owed at least some level of moral consideration. These sentient animals can suffer, and so they at least need to be treated humanely. They are not just pieces of property that we can use or treat as we please. The Ten Commandments, however, only mention sentient non-human animals in the last commandment, and these animals are portrayed as pieces of property that people shouldn't covet when they belong to others. There's nothing at all about the need to treat these non-human animals, or any other sentient non-human animal, with decency and humaneness. Sentient non-human animals may not enjoy the same moral status as we humans do (and if they don't, why don't they?). But even if they aren't as morally important as people, this doesn't mean that they don't matter at all. They do matter morally, and fundamental moral rules must reflect this.
So even if the Ten Commandments get a few of the moral rules right (don't murder, don't steal, don't commit adultery, don't bear false witness), it should be evident that they don't even come close to getting everything right. They simply leave out too much important stuff to count as an adequate list of fundamental moral rules to guide human life.