Such claims come from those who try to play mischief with the meanings of Quranic verses. Shia Islam is not a sect but the real following of the Prophet and his Progeny. Allah (SWT) has granted His prophet Ebrahim (AS) with the title of Shia in Quran (Sura Al-Saffaat: 83).وان من شيعته لابراهيم
Allah (SWT) called the followers of the prophets as his Shia as we read when a follower of Moosa (AS) was in conflict with one of his enemy
هذا من شيعته وهذا من عدوه
فاستغاثه الذي من شيعته على الذي من عدوه (Sura Al-Qasas: 15).
Shia of Ali (AS) are the followers of Ali (AS) who are in fact the real followers of the Prophet Muhammad (SAWA). The most pious companions of the Prophet (SAWA) were called Shia of Ali like Salman, Abu Tharr, Ammar, Miqdad and others. That is why you find many Hadeeths in Sunni books from the Prophet praising the Shia and saying that they will be in Paradise (Al-Haafidh Al-Tabaraani in Al-Mu'jam Al-Kabeer 1:320) and (Al-Haythami in Majma' Al-Zawaa'id 9:131) and (Jawaahir Al-'qdain by al-Samhoodi 294) and (Kanz al-Ommal 12:104) and Al-Salihi al-Shaami in Sobol Al-Hoda Wal Rashaad 7:11).
There are also many Hadeeths in Sunni books that Shia of Ali are the best of all creatures. In Tafseer al-Tabari 30:335 a Hadeeth narrated from the Prophet (SAWA) : Ali and his Shia are the best of all creatures.
Same Hadeeth ( Ali and his Shia are the best of all creatures) is also narrated by Al-Haakim Al-Hasakaani in Shawaahid Al-Tanzeel 2:353 and Soyooti in Al-Durr Al-Manthoor 6:376.