The Quran answers the question for your friend if he would only read further and develop some contextual analysis. He is simply selecting verses he deems fit while disregarding the overall message. You can't selectively interpret verses outside of context:
Certainly the Quran was revealed in perfection and remains perfect. In relation to ma malakat aymanukum, the early Meccan verses understood that sexual relations were occurring between owners and their slaves. More importantly, these early verses understood that virtually no boundaries existed at the time for the sating of one’s sexual desires. Worse, women had no place or value in pre-Islamic Arabia:
“Drunken orgies were commonplace…marriage arrangements were so loose as to be scarcely recognizable. Women were regarded as nothing more than chattel…” – Huston Smith, The World’s Religions
As a result, the early Meccan Surahs decreed as follows:
“…[Those] who abstain from sex, except from their wives or those their right hands possess…” – Quran, 23:5-6 (Yusuf Ali)
“And those who guard their chastity, except from their wives or those their right hands possess…” – Quran, 70:29-30 (Yusuf Ali)
These early verses are not granting permission they are establishing a very clear boundary. This distinction cannot be impressed upon enough. A limit had now been set on one’s sexual conduct as decreed by the Quran in relation to the existing licentiousness throughout the pre-Islamic community.
As the process of revelation moved forward and the first Islamic community formed post-Hijrah the mandates regarding sexual relations were finally codified in the Medinan verses regarding ma malakat aymanukum:
“If any of you have not the means wherewith to wed free believing women, they may wed believing girls from among those whom your right hands possess: And Allah hath full knowledge about your faith. Ye are one from another: Wed them with the leave of their owners, and give them their dowers, according to what is reasonable: They should be chaste, not lustful, nor taking paramours: when they are taken in wedlock, if they fall into shame, their punishment is half that for free women. This (permission) is for those among you who fear sin; but it is better for you that ye practise self-restraint. And Allah is Oft-forgiving, Most Merciful.” – Quran, 4:25 (Yusuf Ali)
“Let those who find not the wherewithal for marriage keep themselves chaste, until Allah gives them means out of His grace. And if any of your slaves ask for a deed in writing (to enable them to earn their freedom for a certain sum), give them such a deed if ye know any good in them: yea, give them something yourselves out of the means which Allah has given to you. But force not your maids to prostitution when they desire chastity, in order that ye may make a gain in the goods of this life. But if anyone compels them, yet, after such compulsion, is Allah, Oft-Forgiving, Most Merciful (to them)…” Quran, 24:33 (Yusuf Ali)
The Meccan verses set a limit, the Medinan verses established the rule. The Medinan verses make clear that consummation is allowed only within the confines of marriage regardless of social status, be it a free woman or a slave. As a result, any interpretation or ruling allowing for sex with slaves outside of marriage is now deemed a sin.