Most Finns seem ok with it. It is one of the best countries to live in, and it is at risk of war with Russia. It is generally thought that any forced participation in war would be due to an existential threat from Russia.
For the mandatory 1 year service, some sort of civil service is possible instead of the full military experience. I think perhaps it facilitates young people to gain independence. It sounds easy to get a mental illness exception if you just tell a doctor youre depressed etc.
I didnt understand it before living there. In my country I couldnt imagine being patriotic, but Finland is actually nice, so I can understand that people would be willing to defend it.