It was abolished to consolidate the New Government and modernize the country's administration and military.

With orders to abolish the han system in 1871, all lands comes under direct government administration instead of vassal system. Then conscription was put in place a couple of years later to build a national army and, which also deprived the samurai of their hold on the armed forces. Finally, the four Confucian classes were abolished.

As for the samurai tradition, well no one's allowed to just cut down peasants as they wish anymore, and a great many had a bad time in the transition from having a stipend to having to find employment. But certainly no one stopped them from practicing other parts of Bushido. And join the army and be officers.

Was it necessary? The leaders of the Meiji Restoration certainly thought so in order to compete with Western powers on the world stage.

Sry on phone. No sources till I get home. Can't remember the books name off the top of my head.
EDIT: Odd. I thought I had sources that went further in detail than my cultural history book and Early Modern Japan. Well I'll go digging in the library if more details are needed.