We, Shia Muslims believe that with out following the real Sunnah of the Prophet (SAWA) no one can be a real Muslim. Rejecting the Prophetic Sunnah means rejecting Quran because of the orders of Allah in Quran to obey the Prophet (Sura An-Nisaa' 59 and Sura Al-Maa'idah 92 and Sura An-Noor 54 and 56, and Sura Muhammad 33, and Sura Al-Taghaabun 12.

'Allah (SWT) Stated in Quran (He who obeys the Messenger, has indeed obeyed Allah) Sura An-Nisa 80.

The main point here is the authenticity of the narrations of the Sunnah. We don't take the narrations from liars or wrongdoers as part of the real Sunnah. We follow the most authentic narrations from the Prophet Muhammad (SAWA) which came through Ahlul Bayt (AS) and the authentic narrators. 
Many narrations were fabricated by wrong governments and their servants for justifying their wrong deeds, still claimed to be from the Sunnah. Muslims really need to be careful in calling narrations as part of Sunnah before assessing the narration and all the narrators.

'A well known Sunni Aalim (Scholar) Dr Tijani Smawi wrote a book after studying and comparing Sunni and Shia books of Hadeeth, stating that the Shia are the real followers of the Sunnah. الشيعة هم أهل السنة. This book is available in many websites. This Sunni scholars has become A Shia and written many books which guided thousands of Muslims to the real Islam of Ahlul Bayt (AS). The I was Guided is one of his famous books.

Wassalam.