When one become a citizen of a nation people agree to abide by its laws.
The people agreed to the Constitution of the Mosaic law which lasted over 1,000 years til the time of Christ.
They did not have medicine against sexually transmitted diseases and the spread of disease would have damaged the nation's health.
The 'shouting loudly' was to show there wasn't consent, and that it was rape and not fornication or adultery.
Remember under the Mosaic law there was not only the 'letter of the law' but also the 'spirit of the law' which allowed for: mercy.