Okay, hear me out. This is in no way me hating on Benny. Although I wasn't a huge fan of him, I in no way hated the character or the actor (I love Ty, honestly. He's great...) 

This is more about how people feel about Sam's views on Benny, and I really feel the need to talk about this because honestly, Sam gets a lot of hate for it and called a hypocrite and jealous. But that is so far from true in my opinion. 

First of all, let's mention the fact that Dean didn't actually tell Sam about Benny. Of course he's going to be suspicious about that. 

But here's where it really gets me thinking. Dean's reasons for trusting Benny.

He saved his life. Sound familiar? Yeah, that was one of Sam's reasons for trusting Ruby and look where that got him. 

He got him out of Purgatory. Okay, I am in no way saying this was what was happening or anything, but it's something you kinda have to think about in my opinion. The way out was for humans only, and the only way any type of "monster" could get out was with a human. Benny clearly knew about this. The only way he was getting out was if Dean gave him a "ride" out, and the only way Dean was gonna do that was if he trusted him. He could've easily been manipulating him all along just to get out f Purgatory. 

Again, I am NOT saying this is what was happening. I do truly believe Benny was a good guy at this point (we do know that before he was killed he did kill a lot of people though...)

But seriously guys. Look at this from Sam's perspective. Dean gets back from Purgatory (after Sam spent a year believing him to be dead) and suddenly he's besties with a vampire, who he neglected to tell Sam about, and his reasons for trusting him sound a lot like the reasons Sam gave Dean for trusting Ruby. You really can't blame him for not trusting Benny. 

People call him a hypocrite for not trusting him (they do the same whenever he doesn't like the fact that someone is working with a Demon) but it's not hypocrisy, it's trauma and learning from his mistakes.

Basically, what I'm saying is that although Benny wasn't like Ruby, the situation can actually be compared to the one with Ruby in quite a few ways. 

Also, there's bound to be some bitterness about the fact that Dean killed Amy (for doing something Sam and Dean would do for each other, and we all know it's true...) and yet when it's his friend and him deciding someone can be trusted, Sam isn't allowed to voice his doubts...