No one cares or will even notice your lack of participation.
Some seeders have amazing infrastructure and can seed in an hour what would take you a year on a residential connection.
This is not an "if everyone did that" problem because not everyone has limited residential bandwidth.
If youre worried about moral obligations adopt a few torrents with very low numbers of seeders to ensure they dont die.
Alternatively, you could rent a seed box for a month and upload 5 years worth.