Why does Henry give so many reasons to support his need to speak out in the Virginia Convention?
One of the reasons that Henry gives such a detailed analysis behind his position is because it was not a popular one. We now view the need to fight England as a given, something that existed beyond question. Yet, at the time when Henry gives his speech, the speeches that preceded his were about the need to not raise funds and militias against England. These speeches were Loyalist, in nature. Part of the reason that Henry gives so much in way of support for his position is because his audience were not in full support of his beliefs. He had to expend so much intellectual and physical energies in defense of his position because it was not a very popular one.
The "war and subjugation" that Henry illuminates necessitates action being taken. Henry has to carve out two distinct realities that were not widely shared. The first is that the need to break free from England has to be seen as an absolute and that victory is only possible if the will to win is present. Both realities were not entirely embraced at the time. It is in this light where Henry had to offer many reasons to the audience in defense of his position.