Not true. Not all Israel was blinded. Only "part" of Israel was. If you study the whole thrust of Romans 9-11 you will see that Paul is comparing the chosen elect (the election) within Israel to those who are "blinded." In Romans 11:1-5, Paul identifies “his people which he foreknew” as a spiritual “remnant according to the election of grace.” This is in complete contrast to the blinded natural majority of Israelis who reject Christ. There is no way they can be deemed God’s chosen people, God’s elect or the people of God, regardless of how loud or often Dispensationalists claim such.
We see this in Romans 9:6-13: “For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, they which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.”
What this is saying is, those who are not saved have no right to consider themselves as true Israel. The apostle here identifies two Israels; one spiritual, elect and believing, the other natural, ethnic and containing both believers and unbelieving. One is true spiritual Israel (“the children of God”/“the children of the promise”), the other is merely “children of the flesh.” Basically: national theocratic Israel was a political entity in which a believing spiritual remnant – true Israel – abode. It is only those Jews who belonged to that remnant within ethnic Israel that were true Israelis in God’s eyes. Through the cross, and since the cross, only those Jews and Gentiles who embraced Christ were enjoined to that remnant that are considered His chosen people. These have been joined together on an equal basis in Christ.