The Pizza is just a sympton. No I dont think someone will go OTD because they cant have Pizza on Motzei Shabbos
But Food can make someone go OTD. I was once at someones house and the kid did not want to eat chulent because he did not want to be fleshig. The father then forced the kid to eat the chulent. I told that story to someone else who went OTD and they told me that is exactly what happend to them. They hated Shabbos for that as it became a struggle to eat the chulent.
Hamaser = Hamavaser, the Israeli Newspaper that photoshopped out the women from the picture .
As far as the higher rates of OTD among the more modern as opposed to the more charedi, IMO the reason is not Kulas as much as its just easier to leave. I cant tell you if the average Satmar loves yiddishkeit as the average Young Israel member, but I can tell you for that Young Israel member can much easier vanish into the greater world without much difficulty unlike the Satmar who has to change their appearence, Accent, social norms etc.
About Lifnei Iver, Even if you keep a certain Halacha (Halacha in the sense where some hold Issur and others Muttar) , you probably also know plenty of frum jews might not keep the same Halacha. I am sure those they keep only Chalav Yisroel are more than aware that plenty of frum jews hold by the O-U and eat Hagaden Daaze Ice cream unlike say Pork where no frum jew would eat.