actually, that site states why they are blasphemers, check it if you want but make sure you check :
http://aicp.org/IslamicInformation/English/WahhabiyyahHistoryFighting.htm
the conclusion on the fighting:
Conclusion
This is a very brief summary of the story of Muhammad Ibn ^Abdul-Wahhab. To talk at length on each of these details would be very lengthy. The tribulations inflicted by the Wahhabis were a calamity for the Muslims. The Wahhabis shed a great deal of blood and robbed a great deal of money; their harm was prevalent and their evil spread.
Many of the hadiths of the Prophet, sallallahu ^alayhi wa sallam, spoke explicitly about this tribulation. One narration said:
which means: <<There will be people who come from the eastern side of Arabia who will recite Qur’an, but their recitation will not pass beyond their collarbones{28}. They will go out of Islam as swiftly as the arrow goes through the prey. Their sign is shaving their heads.>> This hadith was mentioned in many narrations, including Sahih-ul-Bukhariyy and other books of hadith. There is no need to expound on listing these narrations or their narrators because they are well-known and of the sahih{29} classification.
The Prophet said: "Their sign is shaving their heads." This is an explicit reference to the Wahhabi sect. They used to order all those who follow them to shave their heads. None of the previous sects, i.e., those who came before the Wahhabis, like the Khawarij or other innovators, had this sign.
As-Sayyid ^Abdur-Rahman al-Ahdal, the Mufti of Zabid, used to say: "There is no need for writing against the Wahhabis. For, in refuting them, it is sufficient to mention the hadith of the Prophet, sallallahu ^alayhi wa sallam: <<Their sign is shaving their heads>> since no other innovators had ever done it."
It happened once that a women made her point against Ibn ^Abdul-Wahhab when they compelled her to follow them and she did. He ordered her to shave her head. She told him: "Since you order the woman to shave her head, you have to order the man to shave his beard. The hair of the women is her decoration and the decoration of the man is his beard." Ibn ^Abdul-Wahhab could not answer her.
Among of what the Wahhabis used to do was to prevent the people from asking the Prophet, sallallahu ^alayhi wa sallam, for his intercession--although the hadiths about the Prophet’s intercession are numerous and are of the mutawatir{30} classification. Most of his intercession is for the Muslims of his nation who committed major sins. The Wahhabis also prohibited Muslims from reading Dala’il-ul-Khayrat--which includes saying as-Salat on the Prophet and mentioning many of the Prophet’s complete descriptions. They said this is blasphemy. They also prevented Muslims from saying as-Salat on the Prophet on the minarets after the Adhan. Once a righteous blind Muslim was calling Adhan and said as-Salat on the Prophet after the Adhan{31}. The Wahhabis brought him to Ibn ^Abdul-Wahhab who ordered his execution.
If I [the author] was to pursue the mischievous things the Wahhabis did, I would fill notebooks and lots of papers. However, what has been mentioned thus far is enough.