Sky lantern release is an ancient Chinese tradition, as form of homage & a belief in the earthly release of souls from loved ones to the heavens.
In the past, Human population was small, & thus caused little harm. However in this era of 7 billion+ & densely populated Human habitats, as well as the dangers of wild fires, alternatives would be necessary if one still wishes to follow such tradition, eg - unpopulated small islands, etc.
What that is manmade may go up, but it will eventually come down, & alarmingly land on busy streets, Humans, homes, factories, etc, even if littering is not a concern, let alone the already plastic filled seas of Earth.
Also, the weather plays a large part, even if heavier than candles battery operated LED lights are used. Humidity, temperature & winds may cause the balloons to move in unexpected directions, or may not even lift off.
It is grand sight, no doubt, may even bring solace to some, but the dangers & pragmatism to living lives outweighs the benefits....
Ignorance is not a crime, but whomever were the organizers of this event, did not think it thru thoroughly, & worse - collected money from the equally naive. They would need to at least provide refunds back, as well as make good investors funding for such event, pay suppliers or else, they may be considered scammers, & in this period where many had been scammed, they are unlikely to get away lightly with it....