The Quran is clear on having sex with slavewomans. If muslim did not read hadith, they would have followed Allahs word in Quran, " Dont force your slavemaidens into prostitution against their will"
Hadith on this topic is very crazy, and legalize rape with slavewomens, that has just lost their husband in war.
That hadith is talking about quite a different scenario.
Basically, people would tell their slave women to go out, as prostitutes, to earn money for their masters. Muhammad put a stop to that practice. But that and sex with one's slaves are two distinct issues.
That and, there are numerous ahadith that say that slaves should be loyal and obedient to their masters.
Bukhari
Volume 3, Book 46, Number 723:
Narrated Abu Musa Al-Ashari:
The Prophet said, "He who has a slave-girl and teaches her good manners and improves her education and then manumits and marries her, will get a double reward; and any slave who observes Allah's right and his master's right will get a double reward."Volume 3, Book 46, Number 725:
Narrated Abu Huraira:
The Prophet said, "Goodness and comfort are for him who worships his Lord in a perfect manner and serves his master sincerely."Volume 3, Book 46, Number 727:
Narrated Abu Musa:
The Prophet said, "The Mamluk (slave) who worships his Lord in a perfect manner, and is dutiful, sincere and obedient to his Saiyid (master), will get a double reward."