The Brotherhood of Steel, the orginal guys, made it their mission to keep the good pre-war tech out of the hands of others. They still traded with people and they left those alone that didn't have anything they wanted.
Veronica tells us that over time the Brotherhood have made enemies of everyone. That didn't happen because the Brotherhood was all sunshine an lollipops. They pissed eveyone off because they raided and stole from people.
If all you're doing is going by what Lyons does, then you aren't getting the full picture. Lyons isn't the typical Brotherhood.
The reason why in Fallout New Vegas, the BoS seem to be focused on "super weapons" is because the Brotherhood is in such badshape they feel only a super weapon will save them. Energy Weapons and Power Armour simply don't do it anymore. Veronica even tells us this, she says something like "Time was all you needed was a power armour and you could get whatever you wanted." The thing is now other factions have advanced to the point were they can stand up against the BoS and win.
It depends on which chapter you're talking about. The Midwest and Lyon's Brotherhood are not raiders.
The Midwestern Brotherhood are more than just raiders, their extortionists that run a protection racket. They actively went out and built a larger empire (if we can call it that) whereas all other Brotherhood, including Lyons aren't interested in ruling anyone. The MWBoS also used slave labour, put people up on crosses and built gulags.