Modern Hebrew is not different than Turkish or Farsi – it is the language of a secular culture complete with all those things that we want to stay away from. The fact that some of those who speak Modern Hebrew are religious Jews is not different than the language of any country Jews are in where they speak the language of the land. The point is to stay away from the language of the land and only talk the language of the Jew.
The Chasam Sofer writes that the reason Jews do not speak Loshon Hakodesh as a speaking language is because it is inappropriate to use a holy language while enveloped in Tumah, which is our current status. The Rambam writes that a love song in Hebrew is more repulsive to Hashem than the same song in Arabic, for instance, because the pollution of the Holy language is an additional crime. If someone wants to store pornography in his house, thats bad enough. But to store it in the Aron HaKodesh is unspeakably worse. So to cause Loshon HaKodesh to be used as a street language, complete with all the disgusting ways it is used today in Israel, is just more of a reason why we should make sure it never gets into the streets. For our Creator to look down at the world and see His holy language – or even elements of it – used in magazines such as are sold in Kiosks on Yaffo or Dizengoff Street, or spoken by the lowest of the low trying to make a sale, is not something that he or we are happy about.
Modern Hebrew’s origin is actually anti-Jewish. The creators of MH did so because “it is not possible to be a nation without a national language” (see Eisentein’s encyclopedia, ‘Ivrit’). And the changes that were made, both in accent and content, are unacceptable.
So to speak MH is one thing, but to say it is the “language of the Jew” is just not so. Neither is Yiddish the “language of the Jew”, any more than a black hat is the “clothing of a Jew.” But just as the purpose of the hat is “lo shinu es malbushayhen” – we want to dress differently than the seculars – the purpose of Yiddish is “lo shinu es shemom” – we want to talk differently than the seculars.
Maran Hagoen Rav Elazar Shach told American educators that Yeshiva boys should be taught Chumash in Yiddish, even if the boys speak English amongst themselves. He furtermore said that both boys and girls should learn to be comfortable in Yiddish. He also said that Yiddish is spoken by “all jews” (that is his phrase). He referred parents to send their children to Yiddish teaching yeshivos. And there is good reason why Rebbes and Rabbonim give ma’amarim in Yiddish.