They were forced to disband, lay down their arms and merge into pre-existing IDF, specifically because the methods are not acceptable, some of them declined and had to be disbanded by force.
'As head of the Irgun, he targeted the British in Palestine,[3] with a notable attack being the King David Hotel bombing. Later, the Irgun fought the Arabs during the 1947–48 civil war in Mandatory Palestine and, as its chief, Begin was described by the British government as the "leader of the notorious terrorist organisation".'
The targeting the British happened primarily during the holocaust when British were limiting Jewish migration (which has directly resulted in many many deaths).
The history is complex and it is very easy to find reasons to dismiss people who lived through very difficult times and had to make very difficult choices.
Targeting the British during the Mandate was an act of anti-colonization, not unlike other factions that wanted independence from the British at that time, and the Irgun did warn the British before hand but they did not evacuate the hotel which was the central offices of the British Mandate and the Headquarters of the British Army
"Hannah Arendt and Albert Einstein, in a letter to The New York Times in 1948, compared Irgun and its successor Herut party to "Nazi and Fascist parties" and described it as a "terrorist, right wing, chauvinist organization" "
For every war crime from Jewish side you can always point to a similar one from Arab side, this finger pointing is not useful for anything but spurring more hate and igniting the conflict over and over.
Should you decide to be consistent with your logic, then we quickly arrive at human race also being bad and we can end this circus.