There is actually no flaw in the scenario described and no weakness.

After the attacker sends 0.15 btc to his me2 channel through you and closes it, you still have 0.3 btc in channel 1.  What this scenario suggests is that the attacker then convinces someone else on the lightning network to set up a channel/channels with you and send him 0.3 btc through you.  That's fine and that will then deplete channel 1 to a balance of you having 0 in it, and him closing it out.  But two other things had to happen, and the most important of those is that you now have 0.3 btc in a channel or multiple channels with other participants of LN.  You are out nothing and have lost nothing.  The second thing of course is that the attacker had to get someone to send him 0.3 btc.

The accounting behind LN channels balance routing is very easy.  You only transfer some money to another person in a channel you are in if you receive the same amount in another channel (and you can even charge a fee for doing so).