@ujm, you are quoting a machlokes between Reb Moshe and the Chazon Ish. Between the Kitzur Shulchan Aruch and the Mishna Berura.
Are you ready to (theoretically) let a fellow Yid die (חס ושלום) because you chose (on your own) to follow a certain opinion?
Did you ask a rov which posek you should follow? Please confirm with your rov which opinion to follow, and even if he rules like the Kitzur and Reb Moshe – you must have him clarify how to confirm if someone is considered a תינוק שנשבה or not.
Until then, I implore that you lean לחומרא for the mitzva of פיקוח נפשות and לא תעמוד על דם רעך and save and protect every single Yid.
Even if they do not have the din of תינוק שנשבה, we are not permitted to degrade them and slander them חס ושלום.
Eliyahu Hanovi and Yeshayohu Hanovi were punished for speaking disparagingly about Jewish IDOL WORSHIPERS (the real kind) – because “אין הקב”ה רוצה במי שאומר דילטורייא על ישראל”.
(שהש”ר פ”א, ו (א). רש”י ישעי’ ו, ו. ועוד)
The Rambam writes that if such great tzaddikim were punished, how much more so a קל מקלי העולם who dares to condemn so many Yidden as פושעים ורשעים וגויים ופסולי עדות וכופרים בה’ אלהי ישראל.
(אגרת השמד פ”ב)
In these last moments of golus, let’s focus on the positive and holy parts of every Yid.
Regarding the Yidden who are ר”ל temporarily “distant” from Yiddishkeit –
“ראוי להחזירן בתשובה ולמשכם בדברי שלום עד שיחזרו לאיתן התורה”
– thus instantly heralding the coming of Moshiach.
(רמב”ם הלכות ממרים פ”ג ה”ג. ראה הלכות תשובה פ”ז ה”ה, סנהדין צז,ב)