We certainly have the ability to do whatever we want, but is it profitable (helpful) to us? No. Read below.
1 Corinthians 6: 12-20
All things are lawful for me, but not all things are helpful. All things are lawful for me, but I will not be dominated by anything. Food is meant for the stomach and the stomach for foodand God will destroy both one and the other. The body is not meant for sexual immorality, but for the Lord, and the Lord for the body. God raised the Lord and will also raise us up by his power. Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them members of a prostitute? Never! Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, The two will become one flesh. But he who is joined to the Lord becomes one spirit with him. Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body.
The point here is that food is good for the stomach (Lunch/dinner is a natural thing). But sexual immorality is not. Sex is good, in the confines of marriage, which is clearly stated in several places of The Bible is between a man and woman.
As for non-believers who say the Bible is made up, there is plenty evidence of lifelines in historical recordings. The only part, I admit, that requires true faith is the fact that Jesus rose from the dead to save our sins. This is the central tenet to Christianity, and what separates it from all manmade religions. The Bible has everything you need. Those who read it will understand that it has everything sufficient towards understanding God's plan.
2 Peter 1:3
His divine power has given us everything we need for life and godliness through our knowledge of him who called us by his own glory and goodness
I don't think what I said disagrees with what you said. I'm all for marriage. Why stop 3 or 4 people from getting married? There's lots of people in the Bible who had multiple wives. If they are consenting adults why not let them do whatever they wish?