“Since you use your mouth all the time to talk, it’s hard to always be careful not to speak l’h. ”
Yet, those same people dont use their mouth for nivul peh, to talk pritzus or even discuss their own shortcomings (generally speaking). people use their feet all the time, yet they dont go around kicking people.
I dont think it is so much the mouth as it is, what one is used to using the mouth for. just about anyone will tell you, stop using foul language, or stop discussing such a prust topic, but, how many will tell you stop speaking lashon hara.
Watching TV online, is simply the yetser hara convincing you it is ok.