The cause being finite, the effect must be finite. If the cause is eternal the effect can be eternal, but all these causes, doing good work, and all other things, are only finite causes, and as such cannot produce infinite result.
Destructive thoughts and emotions undermine the very causes of peace and happiness. If you think clearly about it, it makes no sense to think you’re seeking happiness, if you do nothing to restrain angry, spiteful, and malicious thoughts and emotions.