I'd suppose that is "common wisdom", because I've read similar things often before.
Nor have I ever read a really serious explanation of the Bible's views toward slavery.
Perhaps its out there, somewhere, but I haven't seen it.
So here goes:
To claim the Bible has "no opinion" on slavery is to miss the entire forest on account of so many trees!
In fact, God hates slavery for His chosen people, it's why he brought them out of Egypt, it's what most of the Old Testament is all about -- Israel's struggles to first escape slavery, and then to eradicate their love of slavery from their own hearts.
Over and over, throughout the Old Testament, God and His prophets remind Israel that their allegiance is owed to Him because He freed them from bondage to humans.
So there could not be a stronger Biblical condemnation of slavery for God's people.
And what is the New Testament all about, if not to make all people who accept Christ into God's chosen people?
The simple fact is that God does not want His people to be slaves to other men, or to sin (note Romans 6:6, Galatians 4:7 & 24).
And the New Testament is also quite clear that God does want His people to be "slaves" to God's law (i.e., Romans 6:18 & 7:25)), to Christ's love, and for those who wish to become leaders: slaves to each other (Matthew 20:27, Mark 10:44).
The New Testament is also clear in condemning slave traders as amongst the worst law breakers.
For that particular gem, I'd invite you to begin reading at 1 Timothy 1:8.
2 Peter 2:19 "people are slaves to whatever has mastered them."
Could there be a stronger condemnation of slavery?
Possibly, but he still made provision in the law for an Israelite creditor to take a brother Israelite into slavery for debt. The Law treats slavery throughout as a fact of life. There is not a hint of it being a sin or wrong.
The Israelites didn't want to be slaves, no more than anybody else did. But they hated being slaves themselves, not slavery.
Joshua enslaved an entire people, the Gibeonites.
I seriously doubt you could hate slavery and slavers more than I do. It is very nearly the ultimate sin, the denial of humanity of a brother human.
But I also don't deceive myself that the Bible contains no single explicit denunciation of the institution. As I've said before, I believe the underlying principles of the Bible point to eventual end of slavery. But the words themselves, unfortunately, don't.
Here’s an interesting compilation of 47 biblical verses referencing slavery.
http://www.openbible.info/topics/slavery
The best way, IMO, to think of the practice in the ancient world, is that it never crossed anybody’s mind it could be abolished. Anymore than anybody in the modern world has suggested getting rid of gravity.
The notion that slavery can and should be denounced, opposed and eventually abolished evolved directly out of Christian doctrine. No other society in the history of the world has come up with the remarkably radical idea that “all men are created equal.”
Today we take the idea so for granted that Christianity and the Bible get no credit for it, which is a shame.