The Netziv reminds you of a Tosefta that you may have missed when he discussed it in Parshas VaYikra (5:1)
וְנֶפֶשׁ כִּי תֶחֱטָא וְשָׁמְעָה קוֹל אָלָה וְהוּא עֵד אוֹ רָאָה אוֹ יָדָע אִם לוֹא יַגִּיד וְנָשָׂא עֲוֹנוֹ:
Why does the pasuk start with the words “nefesh ki techetah?” The sin is not in the act of witnessing something wrong, as described in the first clause of the pasuk, but is in withholding testimony, as described in the pasuk’s ending. The words “ki techetah” should appear at the end of the sentence?!
The Tosefta answers that it’s not by accident that an individual happens to be in the right place at the right time to witness a crime. It’s only because that individual is him/herself guilty in some way, he/she is a “nefesh ki techetah,” that Hashem arranges for him/her to have the misfortune of seeing wrongdoing.
The witnesses who heard the mekalel commit such a heinous act of blasphemy had to participate in meting out justice as a kaparah for themselves, as they had to make a cheshbon hanefesh to understand why Hashem would cause them to hear and see such a horrible spectacle.
Anyone who learns this Tosefta and walks away klerring whether it means you have to actually see the bad thing to be guilty or whether seeing it on a TV screen or a website counts as well is beyond missing the point. I honestly don’t know how to relate to such a vort. You walk down the streets of NY, you ride the subway, you read a newspaper, etc. and you can’t help but be assaulted with sights and sounds that should revolt any normal human being. Maybe it’s a bracha that we have become so desensitized that it makes no impression anymore, because if it did, a person would go nuts. Just the fact that we have to live in such an environment is itself an onesh.
On a positive note, the Tosefta promises that those who are zakai will see zechuyos. When you see someone rushing to do a mitzvah, learning Torah, doing chessed, it’s not just their good deed, but it means you’ve done something right as well to be able to witness such a wonderful occurance.