Your entire post is little more than the justification of bad propaganda.
People look to the media for information, most trusting same to provide the product advertised. When they are fed lies, most take them as truth because of where they read or viewed them. If they knew it was disinformation, they wouldn't depend on those venues. Duh!
While this is true for some, it's not true for everyone. You might be correct in stating that most people trust the media, but a lot of people don't... I belong to that later category and it's not because I think they're liars... it's because they're people (and people make mistakes). So as a former journalist myself I don't take anything as gospel truth without some verification of my own, be it multiple sources, whether or not it makes logical sense and so on. After a while, you start to learn which media channels have better records when it comes to accuracy.
I find ALL the MSM channels (except Fox) are fairly diligent when it comes to journalistic integrity and it makes sense for the very reason you already mentioned... if they weren't so diligent, we wouldn't depend on them.
Sadly, there's another reaction to the media that you missed... Those who seek information not for it's accuracy but for it's support for an argument. I KNOW a lot of people on this site scrounge the media specifically for stories that back up their narrative even if it's not true.
As regards the Civil Rights Act, why don't you visit Mr. Google and take a gander at how many (R)s vs how many (D)s voted for it?
Why would that matter? That bill was signed during the sixth party system when the Democrats were conservatives and Republicans were liberals. (I sure hope you are choosing your party based on your principals not not the other way around.)
The welfare thing was a separate issue, and when he signed it LBJ famously said, "This'll have the n-gg--s voting Democrat for the next 200 years."
Well, he's right so far... and maybe that's why he did it - who knows? I doubt any party can hold its ground for 200 years though.
Fun fact : did you know the predecessor to the Democratic Party was called the Democratic-Republican Party and that people just called them Republicans? That was during the First Party System.
Dynamics my friend, it's a thing.