I partially agree that the 'demigod' worship may have become a disease among a majority of 'Hindus' due to lack of proper understanding. But it is also important to note that 'demigod' worship is legally allowed in 'Hinduism'. It is not wrong but considered to be an act lacking intelligence (covered by ignorance). If vedic texts glorify the 'demigods', we could begin by understanding the concept of a demigod, which I feel is important at this stage.
1) Before I go into discussing about demigods and demigod worship I would like to discuss on something very important - what Dr. Naik quotes and does not quote from the 'Hindu' texts. Example, Dr. Naik quotes Shvetashvatara Upanishad chapter 6, verse 9, that the Lord has no masters, no controllers, He has no parents. In verse 7, He is described as the 'dEvatAnAm paramam cha daivatam' (He is the Lord of all Lords), as the 'God of all gods' and 'Ruler of all rulers'. These are consistent with Islam, so Dr. Naik consistently quotes these.
However, Dr. Naik silently and conveniently ignores verses 10 and beyond, where the Lord is defined as ekO dEvaH (He is the ONLY Lord; there is only one God), sarvabhootEshy gooDhaH (resides deep within the hearts of every creature, every entity), sarvavyApi (the all pervading), sarvabhootaMtarAtma (the inner soul of every soul), sarvabhootAdhivAsaH (the abode of all beings; where all beings rest, reside), sAkshi (the witness who resides in the heart). The subsequent verses call for introspecting this Lord who is in the hearts. These ideas are consistent with other vedic texts, puraNas and Bhagawad Gita but inconsistent with Islamic ideology.
From the Islamic perspective above factors are inconceivable (some of which could even be haram or shirk), because for a Muslim (from the eyes of Quran) God is sitting somewhere in the heavens on a throne as a dictator of this world. This is the key differentiating factor that does not allow other religions to comprehend the 'Hindu' idea of God. Quran does not allow Dr. Naik to comprehend the spiritual nature of individual souls and the spiritual nature of God. So, for a Muslim the concept of 'avatAra' becomes disturbing, because they see only the material side of the absolute truth. As such, Dr. Naik, deliberately ignores these verses and takes up an average Hindu's idea of God and thrashes that viewpoint.
2) Now, to understand what a 'demigod' is: demigods in Sanskrit terms are the devas and the devatas, who are defined as "empowered administrators of material affairs. The supply of air, light, water and all other benedictions for maintaining the body and soul of every living entity are entrusted to the demigods, who are innumerable assistants in different parts of the body of the Supreme Personality of Godhead .... The demigods are authorized supplying agents on behalf of the Supreme Personality of Godhead, Visnu." (from the purports of Bhagawad Gita As It Is, Chapter 3 Verses 11 and 12).
The demigods have specific functions to perform. In general, any element of nature without which human existence is impossible is a demigod. Life cannot exist without Rain, so there is a demigod or personified deity for rain. Life cannot exist without fire, so there is a deity for fire. Similarly deities for air, water, ether, money, wealth, energy, thought, mind, heart, senses, marriage, begetting children, strength, power, death, 'dharma' (justice, laws, righteousness etc) etc etc. Some of these will be important for some and others for others. It is a way to express gratitude for the role an element or a deity plays in one's life - or human existence in general. So, 'hinduism' is a religion of gratitude; being thankful to the nature, the elements, and their deities. But sometimes Hindus have a tendency of getting carried away by this demigod worship.
3) There is no debate on who the 'devas' or the 'devatas' are; they are subordinates of the Lord with specific material duties to fulfill. However there are differences in terms of who the Supreme Lord is. For some Lord Shiva is the supreme; for others Goddess Durga, or GaNEsha, or some others are and so on. But for those who follow Bhagawad Gita and Bhagavatam, there is no doubt that Sri Krishna is the Lord of everything that is there and there is not. Sri Krishna is universally acclaimed by all the great seers as the Lord Himself.
- Sri Shankara acknolwedges that 'KrishNastu bhagavan svayam', Sri Krishna is the Supreme Lord. There is no conflict in the conclusion of Sri Madhva or Sri Ramanuja, except that they take the name of Sri VishNu or Sriman Narayana, who are non different from Sri Krishna as the shastas confirm.
- Sri Krishna says in Gita that whatever one follows eventually follows His path only.
- The vedic texts confirm that a) there is only one truth and the intelligent beings define them varyingly, b) every prostration, every worship reaches 'kEshava' (Sri Krishna) just as every drop of water eventually reaches the ocean,
Part 5 is here: http://gita-god-hinduism.blogspot.ca/2013/05/part-5-dr-zakirs-absolutely-misplaced.html