"You shall not call a conspiracy everything that the people calls a conspiracy, nor fear what it fears, not attribute strength to it." (Yishiyahu 8:12)
From the Judaica Press commentary:
"You of Chizkiyahu's company, even thought you are fever than Shevna's company, you shall not say: We decide according to the majority. (Shmos 23:2). To all that this people that is with Shevna says, for this is a band of the wicked and is not counted, so it is as regards the ten tribes who formed an alliance with the king of Egypt. (Rashi to Sanhedrin 27b)
"The Talmud related that Chizkiyahu himself feared that the group that had joined Sheva and wished to surrender to Sancheiriv actually had the status of a majority and that even God Himself regarded them as the legitimate representatives of the people, and would deliver them into the hands of the king of Ashur. The prophet therefore admonished the people not to consider Shevna's band as a band, or company. Since they are a band of wicked men, they are not counted at all. Only the God-feearing were counted even thought they were the minority. This is a lesson for all generations and all times, that God-fearing Jews should not lose courage nor feel that they are insignificant because the vast majority is not true to the Torah." (Rav A.J. Rosenberg)
Not that I would call non-observant Jews wicked, chas v'shalom. From my perspective, most are either missing important education or have allowed secular scholarship and its biases to misinform them as to the truth of Torah. That's not evil, rather it's unfortunate.
But for those who claim that Orthodoxy needs to change, or that the Orthodox need to stop acting like we "own Judaism", this verse and its interpretation stand as a stark reminder to us that we must have confidence in our beliefs. Even though we are at best 15% of the overall Jewish population, the truth of Torah gives us the assurance that what we are doing is right. Now all we have to do is, through positive example, inspire everyone else to see that.