You can say this because their environmental destruction wasn't enough for you personally to be worse of than them. If that's the case for future generations, they will almost certainly be angry.
Being angry doesn't necessarily equate to being right or rational. A lot of people are really pissed off about climate change and ecological harm and blame previous generations for drilling, mining, polluting, etc... then they happily board a plane to some exotic locale to get a few good shots to post to Instagram.
