The previous post states “litvaks.. in general”. Really? You think that includes Vilna Gaon, Rav Chaim Volozhin, and The Chofetz Chaim etc. These gedolim all write down kabbalah at least in refererence for the klal to be machhezek themselves within their provided context.
With this in mind these holy tzaddikim present their views with open available references and followed to printed the sources publicly. They are many instances of litvishe gedolim maintaining good terms with the chabad rebbeim over the years for example (Third rebbe/Rav Chaim Volozhin – Fifth rebbe/The Chofetz Chaim – Seventh rebbe / Rav Moshe Feinstein)
The basis of the OP is lacking mention of sources kabbalah and/or chassidus, such a critique is obviously baseless. This is a consistent habit of those who have no expereince in such matters. This means the numerous rishonim who write on kabbalah as well.
So again,
Rav Chaim Malinowitz ZTL (editor of Artscroll shas) happens to give shiur in the first chapters of Tanya. With a simple google search they can be found. The rav also gives a yud tes kislev shiur that can be found on youtube.
As far as kefirah, just in Tanya itself there is a chapter titled shaare yichud vhamenuah dedicated to the theme. Please let that be implicit enough, context aside.
To have disagreements thats fine, but to perpetuate hatred within klal yisroel for leisure is a rotten way to live.
וְדָרַשְׁתָּ֧ וְחָקַרְתָּ֛ וְשָׁאַלְתָּ֖ הֵיטֵ֑ב וְהִנֵּ֤ה אֱמֶת֙ נָכ֣וֹן הַדָּבָ֔ר נֶעֶשְׂתָ֛ה הַתּוֹעֵבָ֥ה הַזֹּ֖את בְּקִרְבֶּֽךָ׃
(דברים טו:יג)