In order to shed some light on the answer to this question, a few points need to be made:

1- God has created man in a way that he is constantly seeking to find new facts and gain complete scientific awareness regarding the truth surrounding him. There is not a time that he isn't engaged in some sort of scientific activity or understanding of the truth. Of course, this scientific activity is in conformity with his age and physical conditions and his mental and behavioral domain. In other words, God has put man on the earth with enough resources to reach perfection and welfare and to understand the truth, enabling him to reach his goal and achieve the ultimate objective of his creation through it. The Holy Quran says: “By the soul, and the proportion and order given to it; and its enlightenment as to its wrong and its right;-Truly he succeeds that purifies it, and he fails that corrupts it!”[1] Now, on the ground of this fact that man is the most distinguished creature of God as a result of his ability to acquire knowledge and scientific advancement, how can a person be excused[2] if he does not use theses existential resources for his most fundamental need which is to reach the goal of creation which is a means to please God and he neglects and acts sluggishly and chooses not to go a way which leads to this destination (and contents himself with his fathers' opinions and thoughts and manners and customs whereas he knows that his fathers are not conversant with knowledge and thinking and the manner of their living is not based on the guidance of learning and knowledge). In fact, his behavior is condemned by the same conscience he has neglected, which is his own. Concerning this matter, the Quran says: "Many are the jinn and men we have made for Hell: They have hearts where with they understand not ,eyes where with they see not, and ears where with they hear not. They are like cattle,-nay more misguided for they are heedless (of warning).[3]

2-It is obligatory on every Muslim who considers himself a real follower of Islam, to have some reasoning for his beliefs instead of just blindly following of his fathers. It is because of this that is has been noted at the outset of Islamic laws books which every Muslim is obliged to learn, that it is necessary for every Muslim to believe in the fundamentals of faith with his own insight and understanding, and that he cannot follow anyone in this case, that is, he can not accept the word of another who knows [and has to strive to find the truth by him/herself].[4] Furthermore, the soul of Islam rules is conception and knowledge too and it invites us to think and ponder for ourselves.[5]

Of course, it is obvious that the level of thinking and understanding varies in proportion to the knowledge the individual possesses; it is expected from an illiterate person to give reasons that correspond with his thinking and his life's conditions. There is a famous hadith on this matter that says: The prophet of Islam (peace upon him) asked an old woman spinning thread: “How would you prove the existence of God?”  She stopped working for a moment and said: “Through this.”

The old woman wasn’t able to and didn’t give a philosophical answer and wasn’t expected to either; rather she noted this understandable point for all that if there is someone needed to whirl this wheel, how would not this world need a creator and a director? In another story,  an Arab gave a similar response saying that the track of a camel testifies the existence of a camel, so all skies and the earth will testify the existence of a gracious and omniscient God.[6]

But it seems that the simplest and the most general reasoning for the rightness of Islam is it's conformity with the nature of man. If a person does not put this God given nature under the dark layers of dustiness by sin foul behavior and immorality, he will acquire learning and certainty regarding rightness of Islam and may also use in addition to using his own intellect and thinking as a way to find true beliefs.

3- It is true that one must reach a sure and certain conclusion on the fundamentals of religion, and that the slightest doubt regarding these fundamentals defeats the whole purpose, and that it won’t suffice for one to follow others on these issues and he/she must do research for him/herself and reach a certain conclusion. Nevertheless, this surety and certainty which is the criteria for our beliefs regarding the fundamentals of religion can be acquired through argument and logic, and can also be acquired via listening to Quranic verses, etc.[7]

One of the ways one might reach certainty is through consulting scholars.[8]

What the Quran has reprehended is blindly follow others regarding these beliefs:

“When it is said to them: "Follow what God hath revealed": They say:" Nay! We shall follow the ways of our fathers". What! Even though their fathers were void of wisdom and guidance?”[9]

Verse 104 of surah Ma’idah conveys the same message.

It can be concluded from these verses that if their fathers were learned individuals possessing insight and guidance, they would have been qualified to be followed.[10] Nevertheless, despite the fact that they knew they weren’t qualified, they followed them and consequently, what they did was considered the following of an ignorant person by an ignorant person.[11]

How can one be considered a Muslim while he blindly follows people who are neither men of knowledge and thinking, nor their behaviors are based on divine and natural guidance.  It is obvious that true Muslims are either men of knowledge and thinking, or their behaviors are based on divine and natural guidance which comes through taqlid which is backed by knowledge and comprehension, not bias and grudge. Clearly, if it isn't so, one won't be excused on the Day of Judgment.