Inclusivity

  So, last summer after so many years of not playing Dungeons and Dragons, I am back at it. I run two games and  play in another. I play 5th Edition.
  I have a quandary.
  In the game I play, there is a Tiefling rogue, alignment Neutral. He has been with this group, in game, about 2 weeks. Last session, we found a lovely hoard of goods (coin, gems, paintings, magic items) and he offered to go in and check for traps. Three of the characters decided to insight him and found out he was lying and that he wanted to pocket some of the goods for himself. So, they attacked him to kill him.

1. Tiefling - In 5th edition Tieflings do not have an innate tendency towards evil, though many usually end up going down that path. Tieflings have a fierce independent streak and are inclined towards being chaotic. This Tiefling wants to start a community for Tieflings, since they have such a hard time getting along in the world.
2. Rogues might be ruthless criminals, sly tricksters, deadly assassins, or good hearted thieves who steal from the rich and give to the poor. Whichever way you decide to play one, you're guaranteed to have a number of tricks to help you achieve your goals. This rogue generally steals from the rich or bad. However, he is getting a bit frustrated after a few years of working to achieve this. The urge is strong to accomplish this goal.
3. Most of the players in our group, including the DM, do not like this player. He's new to the game. Too much TV and too many video games have falsely colored his view of what is acceptable in this real world and his social skills are as stunted as a malnourished child. Because of this, the DM squashes his attempts to do things and he allows the other players to meta-game this guy.
4. These few players decided to insight this guy, our trap-finding rogue, when he offered to check for traps on a very large pile of loot. Because they don't like him. Because they are meta-gaming about things that he has said to the DM. Because they thought he wasn't acting like a team player. To be fair, one of them was Chaotic Evil that day. But that's ok.

How is this one get better? As part of the D&D Community, I want to help this person be a better player and a better PERSON. What even does "inclusivity" mean if we don't include everyone?