I believe the official reason for going in was a tip they'd received that the Branch Davidians were stockpiling guns and ammunition. When Koresh and his followers holed up inside, the feds showed no remorse with children being collateral damage as they eventually set about burning them alive after a days-long standoff in which casualties were traded back and forth.

The feds were blatantly disrespectful throughout this too though, at one point using a tank to roll over a fresh grave site.