We all know that genetic diversity in our species (homo sapiens) is maintained by sexual reproduction. Man and woman provide each half of genetic information randomly selected from their own to their siblings, thereby inumerable combinations of gene sets are possible. What if a person (with uterus) can bear a child with 100% genetic information inherited from its 'parent'? At first it won't be a big deal because there are genetically identical twins already. Then I'd like to add another hypothesis that asexual reproduction is more efficient and faster than normal sexual reproduction. If this asexual production continues for centuries, the number of those people who are genetically identical but with different ages will increase, slowly enough to not being noticed by public but fast enough to eventually occupy a significant portions of our society. Half bred may or may not be possible. What do you expect in this scenario?
Well, if the parent has a genetically identical child, first it would always be a female. So the only way for a male to be born would be to have sexual reproduction. (which would still be 50/50). Second, producing a genetically identical child is not going to have much if any genetic drift, (they are identical!) so the 'evolution' of the female half of the species would almost stop for those that gave up reproducing sexually with males. Also meaning that they would still be capable of sexual reproduction for many many generations to come, as long as the male part of the population doesn't die out.
That happens in nature with various species. Research that to learn why it doesn't last, with one or two anomalous exceptions. Our own crops are monocultures and you can see what problema that is causing, and the history of the Banana. Genetically identical mice are raised for scientific study: one challenges do they face?
In general, the species can't adapt to later changes in the environment, or can't cope with normal variation in the environment because of lackmof diversity.
Humans might not have to worry about many of the issues, and is already genetically impoverished (which might be why intellegece took hold: don't need to evolve thicker fur if you can make clothes; we're already unsuited for most environments we live in). But others, such as disease, might be a bigger problem.
JD already hit the tooth on the nail, lack of sexual intercourse means lack of adaptation and quick death. Few creatures survive like this, whiptail lizards being the only one of any real size that comes to mind, and it's thought they will go extinct soon enough, from an evolutionary time scale at least.
Species that can reproduce both asexually and sexually often prefer sexual, and in particular prefer sexual reproduction at times of extreme scarcity/danger such as lack of food when you would think they would be less willing to 'gamble' genetically, because of the big adaptive advantage it gives them.
To stress another side of things, it's not just an inability to adapt to single disastrous things like disease that limits this option. The slower evolution and change of a species is drive by sexual reproduction. A creature can not evolve and grow (much) without it. That means it would be rare for a truely complex creature, like humans, to reprodue asexually because the wouldn't have evolved to that level of complexity as asexual creatures. Of course it's possible they evolved using sexual reporduction and later 'evolved' to be asexual; a short term gain that will harm them in the long term, like the whiptail lizards did.
However, look at the diversity of humanity for a second. I'm a programer, and I'm pretty good at it. However, I'm horrible disorgnized. I need someone else to help me to set a path forward and decide what to priortize, and to interface with the customers to collect requirements. I've created tools which used complex mathmatical analysis algorithms I would never have invented, but I can take the ones others created and implement them. My tools go to other's who are trained and skilled at tasks I couldn't do, despite my building the tools for them. When I go home I have a roommate who is a linguist, I could never learn another language, who often lets me have her left overs because I can't cook to save my life. I make up for stealing her food by being great with kids and often entertaining/watching her son for her.
I'm not helpless, I think I am very good at a number of things, and have done quite a bit to help others, but I'm one man with one set of skills. I survive because others who have skills I completely lack do those, in exchange for me doing the skills I possess. I happen to be as hubristic as the next person, and I wouldn't mind seeing a few others with my skill set, and to be frank my altrusium lol, because I think they are useful and more of them could be used; however, I'll fully admit that a world full of Me's would be a sad place. Assuming we didn't burn down the entire town in failed cooking disasters within the first week our lack of skills and predisposition for certain tasks would leave society helpless when those tasks go undone, or poorly done.
The point is that society works because we have such a huge and different selection of people and skills. A society of only a few people, with their own unique skills and preferences, would be a very questionable society. If we all created clones a few of the most successful would end up in charge, only to later discover that they lack skill sets that the other clones were doing which would cripple them.
In short it's a short term gain that would hurt them in the long term.