is this not the crucial issue, air traffic is going to increase despite all the talk about climate change, and is "ethical investing" really just a cover to allow people to continue with the lifestyle that they dont want to give up. Its easy to beat up on the big bad "ryanairs" of this world, but people are selfish and only care about their own personal circumstances so they will continue to fly unless it is heavily taxed. Flying is also crucial to the global economy, with many people flying to the other side of the planet as part of their job, so paradoxically are you in favour of renationalisation of the global economy with the centre shifting back to the nation state and more products produced locally, like the much derided de Valera vision of ireland .Similarly, regular air traffic is a significant polluter and air traffic is already expected to grow significantly in the coming years. So I don't wish to add fuel to the climate change fire by hoping that Ryanair becomes even more successful that it already is and anticipated to become and that is why I wouldn't personally invest in them.
As regards tobacco stocks, the only reason why smoking and the consumption of cigarettes has fallen off a cliff is because of peoples concerns about their own personal health. If it was simply the case that smoking cigarettes was very bad for the environment but had no health issues then smoking would be higher today than ever just like flying.