I think the key distinction to be made is the one about the difference between normal sadness and depression. As you said it is perfectly normal to be sad after tragic events and medication probably shouldn't be used in this case. However, it seems that this is becoming more common which is not a good sign. Not only does this minimize the suffering of those with severe depression but it places people who are experiencing a healthy response on medication they don't need. SSRI should not be taken lightly because they can be very difficult to get off of without side effects. Also, for many people they only have a mild help and in no way are a sufficient solution for treating the depression. I find the idea that mental and brain events can change each other quite compelling because I know it has helped in my personal case.