Your life causes suffering
You're alive today because your ancestors were killers and survived to pass on their genes. The entire human population owes its existence to ancient actions that most modern people would deem immoral and evil. You're an end with an unjustified means. You can either live in guilt or gratitude to your ancestors. Living with guilt causes more self-suffering. Living in gratitude causes more suffering for others. (The more accepting you are of your ancestor’s way, the more accepting you will be of yourself for continuing the cycle.) Either way, the fact is, simply living causes others to suffer. It can't be helped.
This cycle started the day you were born, and mother went through the pain of labor. (Probably even started before that, with morning sickness, etc.)
The very act of eating is destruction. It doesn't matter what you eat. Even for a vegan diet, there is animal suffering involved during the process of getting plants onto the plate.
No matter what you do, there is suffering caused by your existence. You are permanently stained with this "sin". You can try your best, but you'll never be good enough in your lifestyle or diet to completely avoid causing suffering in other animals and humans due to you being alive.
And that fact weighs on beings conscious enough to realize it. For animals without our sentience, ignorance is bliss.
Being alive means to suffer and cause suffering. Either the eater by going hungry, or the eaten for dying. Such is the nature of life. Humans are always trying to rebel against the way of nature, but will always be a part of it.