I don't understand why any Muslim would say this.
be VERY VERY VERY Careful in calling someone who claims to be A Muslim a kaffir. in fact, unless you have concrete evidence, doing so makes YOU a kaffir. you might even go further and let the Ulema make those statements as they are better qualified to make those judgments.
we have a belief system in Islam, when you become a Muslim, your Islam is based on the 5 Pillars of Islam. Shii'ism is NOT built on those same pillars! they have a different set of beliefs. ergo, Shii'ism is NOT Islam, HOWEVER, you don't pronounce takfir on ANYONE without proof. even then, better to tell the brother or sister that their beliefs are not Islam and try to guide them to the truth. you don't know, MAYBE your or my explanation of Pure Tawheed didn't make sense to them because of fault in our explanation. give them guidance, make dua for them but i would hold off calling them a kafr.
the best advise is to learn your Din. if you understand Islam and especially Tawheed, you will recognize error when you see it or hear it.
the muftisays line isn't bad, and i wouldn't call it terribly long either. you MUST understand these things in order to properly convey Islam.
Br Bilal Philips covers this in his series of lecture entitled: Foundation of Islamic Studies. you caqn download them here, they are at the VERY bottom of the page (ad if you think muftisays was long, this set runs over 17 hours):
http://www.bilalphilips.com/bilal_pages.php?option=com_content&task=view&id=288
Sh Abdullah al-Farsi also covers this topic in his series of lectures on the 6 Pillars of Faith:
http://www.qsep.com/EemanDVD/index.htm
and revisits it on the one on Shirk:
http://www.qsep.com/dvd/fourfoundations.html
you may also take a course based upon Dr Philips work at his free online course here:
http://www.islamiconlineuniversity.com/opencampus/
you can't understand Islam without understanding Tawheed and Shirk. ONCE you understand Tawheed, it would be like someone saying something that is against Surah Ikhlas, you simply KNOW it can't be true! Shiias give the attributes of Allah to their Imams, which would be shirk in Tawheed al Asma wa Sifat. some even go further than.
if you are ever in Seattle, i have all those lectures on dvd and i pass them out freely all the time. but please take the time to learn about our Fabulous Religion that Allah gave us through Rasulullah, Salla Allahu Alayhe was Salaam! it can only bring benefit, In Sha'a Allah!
