Hi, I'm guessing you may be referring to poltical Salafis who take matters in their own hands (this is rebellious towards teir own Islamic Law), if you are referring to very religious people who beat up innocents, am I right? Salafis are often very political as well as religious and some of them become take matters in their own hands despite the religious leaders forbidding this in the cases of Sunnis (Salafis are a group derived from Sunni Islam, so they are Sunnis too, just a different type of Sunnis, as there are many types).
Some groups of Salafis remain actively a-political, because they do not believe that humans can change the world to their liking, so they refrain from all politics (including beating up innocent people) and are waiting for the return of 'Isa (Jesus) who would correct their affears perfectly.
However the Sunnis (which Salafis are too) aren't allowed by the Islamic Law that they're claiming(?) to be following to take matters in their own hands and in any case beat up innocent people (only self-defence would be allowed), so they're taking matters in their own hands in cases like these. If they were in their own imaginary Salafist Shari'ia state, they would receive a physical punishment for the violence. What kind of punishment, depends on the interpretations, as there is no "one Shari'ia" that everyone believes to be true (which is also why some groups of Salafis remain a-political).
People may have the impression that the violent or political people have most knowdedge on their religion - this is the intention to cause division between different groups of people to make people believe that - but this isn't true. I have noticed terrorists tend to have quite a shallow knowledge of their own religion, unless they have made new one for themselves (which is my view). Most of the time those who take matters in their own hands and become terrorist have the most shallow knowleedge about their religion, no matter how "pious" they may look in their thobes etc. They follow a political ideology.
I'm also very religious too, but I'm not a Salafi, let alone a political Salafi. I'm purely Quranic and a-political too, for other reasons. We have many movements and denomonations, and of course different individuals who believe in different interpretations. I know people claim there is only one Islam, but it's not true at all. The only common thing in the different ways of Muslims is monotheism and the Quran if I put it in the most simple terms.
Salafism/Wahhabism is an ideology that was created in the 1700's Saudi Arabia, and is still being funded by them all over the world, despite their current young Crown Prince being against the ideology. However this ideology ended up causing a lot of harm to Saudis too (as the Mecca and Medina are the main targets of the terrorists). The currect Crown Prince of Saudi Arabia, Muhammad bin Salman, has in his modernization era said a lot of things about banning things that lead to Salafism, as it's been a dangerous political ideology for decades now that Saudis too have suffered from quite a bit.
If they are not Salafis, then they the same still applies, they still take matters in their own hands - I guess for political reasons, how else. But my guess is that if they are very religious and political, they are political Salafis. Salafis "suffer" from the saved-sect-syndrome, and therefore have caused a lot of harm to all the other types of Muslims in everywhere where the political Salafis are. I'm also targeted by Salafis because I'm not one of them. What they hate most is not Jews or Christians, but "heretical" Muslims. They (the terrorists) have caused the most harm to normal Muslims in normal Muslim majority countries. Not all Salafis are terrorists, but as it's often said all "Islamic terrorists" are Salafis from their different Salafi movements.