Why have those who decry against capitalism not created something better to replace it with?

Capitalism exists because it is functional. A total barter system is not functional or fair. If I was a farmer and I had a surgeon cure my son of whatever by a procedure, how would it be equaled? If it was said to be equal to 460 pigs, if I had that many it might be more than half of my stock. If the surgeon took them as payment now he/she has the burden of either trying to barter them for good, which will only work if the person he needs goods or services from needs some pigs, until then, he/she now has the expense and effort to feed and care for his/her ”money” (the pigs). If another person needs an operation, and all they have are pigs, then they cannot pay for it because the doctor already has more pigs than he/she can use. Having a standard currency which suits supply and demand that functional, and is easy to track, works. Yes, those who understand it better or know how to work it will make more, but what is there better? There have only been a few alternate systems but none of them has lasted unadulterated, if at all, or not felt the tinge of capitalism; that being the case, why do some people rage against capitalism as something evil when there is nothing better (at the moment) to replace it?