They come to learn, but not to teach.

Question is ha-Kodesh Baruch Hu according to this gentleman stated that He did not want the Erev Rav. Now, to tell you the truth. I have to admit, I don't recall this statement, so I'll take your word for it but it's only a figure of speech. Because the Gemara does say that we want geyrim. But it means that there are two attitudes. You should have taken them with great caution and once you accepted them you should have made certain that they exercised no authority. They come to learn, but not to teach. If a ger comes in to teach, then that's the wrong kind of ger.  (Rabbi Avigdor Miller, "The Keg and the Serpant." #052, 1:02:38)

[You can argue the same with BTs from highly assimilated homes]