Notice that anyone only saying "We must immediately stop Technology's advances against Nature and our freedom!" would be ignored. And, you say, because Kaczynski did something beyond only that, because he utilized violence to air that message more widely, that is the reason he was not listened to.

So, effectively, he was disregarded because his message was that technological progress must be stopped. And anyone with that message will be marginalized, disregarded because "a lot of people have said that". And disregarded also because, "a lot of people in history have always felt tech was a problem" - which means it isn't a problem and we can just let the development of technologies proceed (to wherever they wish to take us).