Frustration

I'm so frustrated and sad, right now.
Why is it so difficult for people to be honest? It's the fucking internet, man. What's the worst that can happen, if people don't agree with your opinion?!
I don't know what to believe, sometimes. I can't stand it when people are like telling you something, agreeing with you and then you see somewhere that they state the exact opposite opinion about the same thing and then I'm like what the fuck?!
It's not that difficult to state your opinion, even if it's different from a good friend's.
It just makes me feel a couple of things; betrayed because if that's the case...if people are such push-overs, then can I really trust them? And pissed off because even if people don't agree with me about something, I really don't see the 'danger' of stating that to me. It's the way that normal people have conversations about stuff and sometimes educate each other.
The weird thing is that I know that if I ask about it, I'll get told that what I was told the first time, is what's right and the other opinion is just stated because it'd suck not to or something.
It saddens me because I'm starting to think that I don't know what to believe. I don't want someone who just tells me what I want to hear. I want someone who can have a debate/argument/fight with me, because they believe something very strongly and not someone who will just shrug and go 'okay, whatever you say', simply because I have a temper and will state my opinion. It insults me, actually.
I know it was just a little thing and it shouldn't matter to me, but it does because it says something about the whole interaction with this person and it scares me shitless that an opinion can change like that or that I'm not told the truth.