In order to answer this question, a few points need to be made:
1- If what you mean by “Shia” are the wrong and unacceptable acts that some Shia do, it is unfair to relate these wrong acts to the entire Shia school of thought; that is because Islam and the Shia school of thought aren’t the ones with deficiencies, it is us the Muslims and sometimes the Shia who misrepresent them.
2- What are your criteria for a religion that is on the straight path, and in other words, what true religion are you comparing the Shia school of thought with that gives you the conclusion that it is a wrong one that has strayed?
In these matters, the Quran and tradition of the prophet (pbuh) (of course, the traditions that are for sure and authentic, not all of them) need to be our main references and touchstones. Any religion or sect that contradicts them is wrong, and any that is in harmony and in accordance with them is the straight path.
Now if you have compared the Shia school of thought with the Quran and tradtions, you need to specify which parts of it don’t coincide; is it their beliefs, their fiqhi rulings, or their moral guidelines? Why is it that the Shia school of thought is accused of being astray just because it is based on following the Ahlul-Bayt with the heart and through words and actions?
Please tell us if you see any contradiction between the Ahlul-Bayt’s sayings and the Shia school of thought’s beliefs.
Shia scholars say: “We don’t follow any way other than the way of the Ahlul-Bayt, because we have learned from the Quran and traditions that:
a) The prophet of Allah (swt) couldn’t have left the Muslim nation without appointing a successor.
b) According to authentic sources and evidence, the one to take his place who was personally appointed by him was the Commander of the Faithful, Ali (as).
c) Others other than the Shia (like our Sunni brothers) have no proof for the prophet appointing anyone other than Ali (as).