It's good that you can see your mistakes and know what you should have done differently. That's how you improve. The wards would not only have given you the peace of mind to push mid tower, but also advance warning to your team of which way Viper was heading.
You definitely weren't completely responsible for the loss, you guys lost as a team in game and in the draft. I can however see how your teammates would be upset with you, as you left them to fend for themselves until both teams went 5 man (22 minutes or so in). You played well once the game advanced to 5 man, so good job there.
Yeah, they're random people you probably won't ever play with again. I'd say in most cases ignore them. It depends how they phrase what they say. If it's "you're shit" or more likely "your shit" lol, without anything explaining why, then ignore them. If they give you advice (coupled with shit talk), try and understand why they are saying what they are saying. Are they only looking for someone to blame, or is there a legitimate point they are making?