I guarantee you, if they want in badly enough, they’ll get in — without or without the kiruv movement.
Do you not recall the story of the “kohen” who wanted the fat tail of the korban?
There was no kiruv movement then… Unless, of course, we’d like to call our naviim as kiruv leaders, which they were.
They may not have been inviting people to their Shabbos tisches, but they were spreading the word of Hashem in a dark and sinful world. The entire Nach is about people who were worshipping Baal and committing the most heinous of averos.
Eliyahu HaNavi had to orchestrate a drought in order to for the people to be willing to listen to his words, and then he had to demonstrate the greatness of Hashem.
He didn’t just ignore the Yidden who were far away.
We Jews are one organism. You can’t let the foot get cut off and expect the rest of the body to not suffer. At the same time, you can’t let gangrene spread up and affect the rest of the body.
Kiruv has to be done carefully, with guidance. But it has to be done.