Is following one's whims and desires (hawa) that deter one from religion considered unforgivable polytheism (shirk), and is the mixing of good deeds with bad a result of following one's whims and desires and worshipping out of ignorance?

The degrees of following whims and desires (hawa) vary. It may lead its owner to major shirk (polytheism), or be limited to minor shirk, or it may be merely a major or minor sin. Not all following of whims is shirk. The Deity (Allah) is He who is obeyed and not disobeyed. So, whoever associates a creature with Allah in any of His divine attributes has tarnished his sincerity and diminished his monotheism. The Sharia may describe many sins originating from the whims of the soul as disbelief (kufr) and shirk, yet they do not expel their perpetrator from the fold of Islam. This is what is called "kufr without kufr" and "shirk without shirk." Faith increases with obedience and decreases with disobedience. However, if following whims leads its owner to major shirk, his deeds will not benefit him unless he repents.