I alwas assumed it worked on a circular principle of "Where are the flowers? - Look where the girls are - Where are the girls? - Look where the men are - Where are the men? - Oh, look, that's where the flowers are (in fact, that's where everybody is, girls included)" so I never thought of the flowers as being given to the men to encourage them to fight. It was more that the men dragged everything else after them. But I think the intention was probably to evoke as many flower/war resonances as possible (rather than, pace nineveh_uk, to scold the young for profligate picking of daisies).