What's your opinion on not reporting if you have no evidence?

I just had a game and afterwards someone on the enemy team requested we report two players on their team for flamming all game. They seemed kind of upset, claiming this is why the community is so bad, when I informed them of my personal policy on a report that relies on chat logs that if the player(s) in question didn't say anything in all chat where I can see then I won't report. Do others agree with this policy?