One shouldn't have to elaborate but briefly, I shall attempt to clarify matters.
Perhaps most importantly, one must consider the times. The WWII era was the most incredibly violent, and the most devastating, both to humankind in general and to Jews in particular, that we've ever experienced, at least to my knowledge. Irgun, et.al., were a part of that general horror.
Irgun and Stern gang were never more than a few thousand people, out of the 600,000 or so citizens of the Yishuv (the Jewish community) within the Mandate, and they were disarmed once the Israeli government was established. Their terror tactics were horrendous and were widely deplored by the majority of the Jewish community, as indeed by the world as a whole.
However, their actions also saved many thousands of Jews from the Holocaust and helped liberate the nascent state of Israel from the British.
Like everything else in life, history's view of them will be more nuanced and complex than is sometimes convenient for the purposes of propaganda. Perhaps this will also prove to be true of Hamas.
Irgun and Stern Gang differ from Hamas in that they were NOT an elected government and they were neither trying to destroy the British Empire or their Arab neighbors, and nor were they inspired either by the racist hatred combined with religious fervor which is apparent within the covenant of Hamas.
Irgun/Stern Gang had arisen in the '30's in response to the really dreadful violence within the Mandate, attacks against Jews by Arabs, but also by British policy that was exacerbating the already hopeless situation confronted by European Jews, by the British blockades during and after the war. This is not to excuse the unforgiveable, but it should at least put their behavior into some perspective. The Jewish residents of the Mandate had come under repeated violent attack, the Holocaust in Europe was decimating European Jewry, and the British were exacerbating the problem. Nevertheless, the Irgun leader David Raziel was killed in the service of the British, having volunteered for a dangerous mission in Iraq.
To quote the article linked below,
"From 1940 through 1943, Irgun declared a truce against the British, and supported Allied efforts against Nazi forces and their allies in the area by enlisting its members in British forces and the Jewish Brigade. A small group lead by Avraham Stern, who insisted on continuing to fight the British, broke off and formed an independent group, Lehi. In 1941, the Irgun leader, David Raziel volunteered for a dangerous British military mission in Iraq to capture or kill Amin al-Husayni, but was killed by a German bomber before the operation could be finished." Amin al-Husayni, or Husseini, was the notorious Mufti of Jerusalem who had begun contacting Hitler as early as 1933, was responsible for much of the violence in the Mandate, and had overthrown the moderate, pro-British government of Iraq enroute to Berlin.
Hamas, on the other hand, IS the elected representative of the Palestinian people, they do have as their stated goal the destruction of their neighbor, and it is unlikely that they will, if only because of their religious orientation, moderate and fold themselves into a nonviolent governmental entity. Upon several occasions recently they've reconfirmed their opposition to the existence of Israel.
Finally, Israel is NOT the British Mandate. The Mandate was a temporary arrangement, granted to the British Empire by the League of Nations, over the Palestine Mandate - which at the time included Jordan, all of which was to become the Jewish homeland. However, the British partitioned Jordan, 78% of the Mandate, and gave it to the Hashemites of Saudi Arabia. Jews were then forbidden to purchase land or settle east of the Jordan, and further Jewish settlement and land sales were severely limited at the very time the Jewish people were in their most desperate trouble.
Israel nevertheless survived. She is not a representative of anybody's colonial government but is a sovereign state, whose very existence should not rely upon the recognition of a terrorist organization that has murdered hundreds of her citizens, and maimed and bereaved thousands more.
I hope this makes sense.
http://en.wikipedia.org/wiki/Irgun