Complex sentence: Some who want to keep the dividend tax as-is claim it is unfair to tax income generated through active work at a higher rate than income generated through less active means or that companies may not have paid their full share of income tax.
Split into simpler sentences: Some who want to keep the dividend tax as-is claim it is unfair to tax income generated through active work at a higher rate than income generated through less active means. There are also worries that companies may not have paid their full share of income tax.