Think Big:
As I have quoted the Chazon Ish in Hilchos shechita, and as others have quoted what are probably similar views of his from his other writings, today we must talk gently, as they will interpret harsh speech as violence, (which implies al achas kamah vkamah that violence itself is forbidden. The Chazon Ish says that the halachos of moridin vlo maalin only apply at a time when hasgachas HKBH geluyah l’ein kol. (When hashem’s providence and control of the world are apparent to all. In those times, aveiros were clear cut rebellion.
But the Chazon Ish provides no makor and no hesber on this statement. Let me offer a hesber. The Rambam says that before a navi is believed to be a navi, he must authenticate himself. That means he must be tested and pass. The test is that he must make predictions and mofsim that come true exactly as he said. The Rambam says this can be done multiple times if we are not convinced. We can give him more tests. (He says we should not overdo it, but he doesn’t seem to say a specific number of times.)
After a person has been shown that this navi actually says the word of hashem, he must obey. However, in our generation, we have no nevuah, and therefore if you go over to a frei yid and tell him he must keep shabbos and start screaming at him, his first question will be why should I believe you that you are right. Even if you throw around all the names of all the biggest gedolim who say to keep shabbos, his response will be a) I never heard of them, or b) who said they are right.
And you know what? he has every right to do so. Why should he believe some stranger on the street who is screaming at him? If you are prepared to make a mofes for him or predict the future, then please do so. If you are unable to do so, you have no right to scream or hit. Pinchas only applied in a totally different generation. In today’s generation, the only way to get somebody to keep shabbos is by gentle motivation and teaching by example.
Maybe this is pshat in the Chazon Ish.