The theory makes three basic sets of assumptions. The first is that liberal women are more likely to practice abortion than conservative ones. The second is that political views of the children are not absolutely determined by the environment they are raised in, and will often swing wildly relative to their parent’s views until they age to a state of maturity, but they are influenced by their parent’s views. The third is that children’s political views at this point tend, on average to reflect those of their parents by the time they become regular mature voters.
The effect of this is that the practice of abortion tends to erode the number of potential liberal voters entering the population. Conservative women by comparison are less likely to have abortions, and thus are more likely to introduce more potential conservative voters into the population. Stated more tersely, those groups that perform abortions are more likely to have declining populations and thus a declining amount of voters maturing with matching political views.
The first assumption in the theory holds out according to teen abortion statistics available online (see link). There does seem to be a correlation between the percentage of recorded abortions and how a state voted in the 2000 Presidential Election. The states with the highest abortion rates were overwhelming carried by Gore, with only 5 of the low rates voting the Democratic ticket. The WSJ has already graphed out the data –

They readily indicate that the correlation between the measure of a Gore victory and the linear trend is roughly 50%. However, the Roe Effect is envisioned as having been building in influence (and ongoing) on Liberal populations since 1973 when the SCOTUS issued it’s ruling.
Interesting theory – what say you denizens of SD.net? Agree or disagree and why?