True, but not strongly enough to make them switch parties. While the number of voters who are against abortion may be about half of the county, only a subset of those voters care enough to make it an important issue to them.
On the other hand, the voters (especially women) who are pro-choice take Roe very seriously and would easily defect to vote for a democrat that they have nothing in else in common with, if the Dem would vow to protect Roe v Wade.
If the Republicans embrace this decision and campaign on trying to overturn Roe v Wade then the Dems will put on beating on them in 2008.
I’ve read that among single-issue voters on abortion, the anti-abortion voters outnumber pro-abortion. Not by a whole lot, but still.