Message integrity attacks are very dangerous because of their ability to destroy the value of communication for everyone who can not afford to "defend" their message against all possible attackers. (Since "defending" a message is effectively impossible, that's basically everyone.) Moreover, the "gains" of such integrity-attacking schemes are themselves marginal, as compared to the damage they can do.
Unfortunately, message integrity attacks are also very subtle, taking advantage of weaknesses in our physical intuition, weaknesses in our understanding of communication ethics, or cloaking themselves in fancy-sounding technology while downplaying the effects of such technology. Even otherwise well-meaning people will defend some integrity attacks, especially when they seem to be a way for the Underdog to strike a blow against the people in power, a narrative we Americans have a weak spot for. The best way to combat this is to acquire a clear understanding of what message integrity is, and to defend it where ever we see it under attack.
In the long run, the only way to have true Free Speech is to allow everybody to speak their messages with the assurance that it will be transmitted with integrity. Free Speech is only guaranteed when nobody has the ability to alter our messages without our permission.