Is ancestry destiny?

You shall not bow down to them or serve them, for I the Lord your God am a jealous God, visiting the iniquity of the fathers on the children to the third and the fourth generation of those who hate me (Exod 20:5; par. Deut 5:9).

Does the Bible teach generational curses? This is a popular prooftext for that position.

Does this envision a fatalistic scenario in which God has hexed a family line so that every descendant is doomed to suffer misfortune?

Punishing descendants for the sins of their ancestors seems unjust. Commentators offer different interpretations of this commandment (or prohibition) to relieve the apparent injustice. 

i) One question is the significance of the "third and fourth generation." 

a) On one interpretation, that's an idiom for "whatever number" or "plenty of."

b) On another interpretation, it denotes extended families–children through great-grandparents. The fourth generation represents the outer limits of the normal human lifespan. 

ii) There is sometimes thought to be a contradiction between this verse and Deut 24:14. However, Exod 20:5 is providential whereas Deut 24:14 is jurisprudential. Exod 20:5 is about something God does, whereas Deut 24:14 is about something human judges do. Roughly speaking, it's a difference between sins and crimes. The latter fall under the human administration of justice (i.e. the Hebrew justice system), whereas the former involves God acting directly or through ordinary providence (e.g. history).

iii) On one interpretation, this refers to remedial punishment rather than retributive punishment. That's possible. However, that distinction doesn't address examples like the collective punishment of Achan's family–which some commentators invoke (see below).

iv) On another interpretation, this involves the principle of corporate solidarity and collective responsibility. And we certainly find that principle in Scripture.

However, that amounts to a disguised description rather than an explanation. It essentially paraphrases Exod 20:5 in terms of collective guilt. But that only pushes the question back a step, for that, too, raises the specter of injustice. By itself, it doesn't give a reason for why later generations should be held accountable or liable for the misdeeds of their forebears. So, if the intention of that interpretation is to relieve the apparent injustice, it fails to solve the problem it posed for itself.

That doesn't mean corporate solidarity is necessarily unjust. But merely that invoking that category is not a solution in itself. The category itself must be defended, if that's deployed in theodicy.

v) Another interpretation is that God punishes subsequent generations who repeat the offenses of their forebears. On that interpretation, God isn't punishing the innocent. Rather, they take after their parents and grandparents. 

Although that's an appealing solution, it's not without problems:

a) One issue concerns the grammatical object of "those who hate me." Does that refer back to subsequent generations, or to the fathers? I don't find commentators discussing the syntactical question. Unless subsequent generations are, indeed, the grammatical referent, that interpretation is stillborn. 

b) Moreover, it seems rather trite or banal to say that God punishes those who hate him. Isn't that a given? He punishes the disobedient.

c) Furthermore, that fails to explain why it's to the "third and fourth generation"–especially in contrast to the "thousandth generation" (v6).

If God is only punishing the generations that continue to hate him, then that could end with the second generation or extend to the tenth generation. It depends on how long subsequent generations hate him. The punishment stops when the last impious generation dies off. 

Likewise, why use more restrictive language for duration of punishment (to the third and fourth generation) than the duration of blessing (to the thousandth generation) if the differential factor is who loves him or hates him?

vi) A final interpretation says this refers to descendants who suffer the consequences for their forebear's misdeeds. I think that explanation is in the ballpark, but it could be made more specific. 

I suggest we look to the book before Exodus, as a frame of reference. In particular, the history of the patriarchs. 

God calls Abraham out of Ur. But Abraham is by no means the sole, or even primary, beneficiary of God's selection. Abraham takes his wife and father with him. 

And consider all the inhabitants of Ur whom God didn't choose? They were left in darkness.

God makes Isaac rather than Ishmael the child of promise. That has generally beneficial consequences for Isaac's descendants and generally detrimental consequences for Ishmael's decedents. 

Likewise, God favors Jacob over Esau. That, too, has generally beneficial consequences of Jacob's decedents and generally detrimental consequences of Esau's descendants. What happens to the ancestor impacts his descendants. 

They veer off into a life apart from God. A tribe or clan that's diverted into a godless existence. They develop their own subculture. Their own social mores. Their own religious beliefs and practices. That's hard to break out of. 

When groups fork off and go their separate ways, the members of each group become more alike in their outlook and behavior. For instance, endogamy makes people culturally as well as genetically ingrown. 

For better or worse, that internal development becomes entrenched tradition. Consider the gypsies, with their distinctive customs and honor-codes. 

In modern times, some localities are more Christian while other localities are more atheistic. What groove you are born into tends to set the pattern for your own life. 

Consider the history of the Edomites. Having branched off, the Edomites become enemies of Israel. 

I expect that's the sort of thing that lies in the background of Exod 20:5. The threat is tersely stated because that's tacitly illustrated by the past and future history of affected people-groups.

Of course, Scripture also bears witness to God's gracious intervention. God can, and sometimes does, break the vicious cycle. Ancestry isn't destiny.