The morning after pill goes a lot further than just preventing pregnancies.
It will probably encourage people to engage in unprotected sex.
The people inclined to use that pill, are already inclined to have sex. What you're trying to stop is not them having sex, since that does have more to do with the home and parents than what contraceptive options are available, but you're trying to prevent a pill from being freely available that would, when coupled with a youth's typical delusions of immortality, will probably result in higher instances of sex without barrier method contraceptives.
The thing here is that the morning after pill is being presented as a solution when it is merely a patch. The real solution is going to come out of the home, and the morning after pill will only make it that much harder to ensure the safety and well being of your children.
I agree with you, and these Senators who voted against it.
If it were to be treated in a manner such as alcohol or tobacco and age-restricted for purchase I would be more comfortable with it being OTC.