why is the bureau of alcohol, tobacco, and firearms, not just rolled into the FBI or something? and why are alcohol and tobacco stuck in with firearms?
Because the BATF began as a revenue enforcement arm of the US Treasury. Most gun control began as a taxation scheme, because it was widely held at the time that the Second Amendment was an individual right and that gun control for the sake of gun control was patently unconstitutional. So you had to come up with some other 'guise' to effectuate gun control.
The solution was to pass gun control laws under the 'color' of revenue measures by taxing the manufacture, transfer, or sale of firearms. Congress had the authority to raise revenue by taxing anything it liked, but gun control would be unconstitutional. Once you had a nexus to revenue, you could also pass all reasonable and necessary laws to effectuate the collection of this revenue. Enter gun registration.
That's how we got the National Firearms Act, the first major federal gun control legislation, which did not prohibit machine guns, it taxed them and was part of the IRS tax code.
Someone is obviously against gun control in here
The BATF has a notorious reputation for this kind of stuff. Seizing the collections of legitimate collectors, forcing them to go to court in order to get their guns back, going in like gang-busters into publicly advertised gun shows open to the public, forcing everyone in the place to give their names and addresses, inspecting every gun on the premises, because there 'might' be an illegal gun some where.
It would be like federal authorities raiding at gun-point a publicly advertised computer show just to look for some bootlegged CD's which they have no other probable cause to believe exists except that 'some times that kind of thing goes on at these computer shows.' Some years ago now, a federal judge ordered the BATF to stop raiding gun shows unless they obtained a warrant for this very reason.
The BATF's notorious behavior and penchant for sensationalism is the reason Senior House Democrat John Dingell of Michigan in 1980 had this bit of flattering commentary on the BATF:
"If I were to select a jack-booted group of fascists who were perhaps as large a danger to American society as I could pick today, I would pick BATF. They are a shame and a disgrace to our country."
They have improved in recent years, after having their budget cut, and threatened with more far-reaching sanctions, but that isn't saying much.