You also say that someone who declares belief in God and Prophet AND knowlingly commits a sin is a Muslim.
I'd say 90% of the non-elderly population of Pakistan skips most of their namaaz. Do you feel entitled to declare all of them non-Muslims?
If you say that not saying bismillah over your food before eating it is not obligatory, then in your opinion - is praying five times a day also non obligatory?
You are confused.
According to the Shafai School, reciting bismillah over an animal as it is being slaughtered is only preferred, not obligatory. It's not my personal opinion...its the opinion of one of the most renowned scholars of Sunni Islam. To the best of my knowledge, there are no schools of jurisprudence that don't consider namaaz obligatory, which is why your example is utterly bogus. Next thing you know, you'll be comparing the consumption of non-zabiha meat to murder and adultery.