I, personally, never liked the pacifist post-war constitution, PERIOD. The Post War constituiton was not written by the Japanese, but it was imposed upon the country by MacArthur and the US Government. The generations of Japanese at that time merely maintained it due to the self imposition , it is not a natural for Japanese to impose such inhibitions.
I want to let you know that those protesters even if they seem 'a lot' are not really that much. What is 40,000 Compared to 128 million? Most Japanese, majority of Japanese support the LDP, Komeito and other alliance parties. This is the reason why LDP Alliance has over 3/4ths control of the Japanese bicameral legislature.
And you need to know that most Japanese , majority, do not like to 'protest', that is a trend common for liberal leftist socialist leaning folks. Most of the protesters are communist members, btw. LOL.