I can hear someone not accepting the shechita of a meshictsan. But why reject the shechita of the majority of Lubavitchers who aren’t meshictsan, especially if you know that a particular Lubavitcher shochet isn’t a meshictsan.
On top of that, the major kashrus organizations, including OU, certify meat that is produced by various kosher meat producers that employ Lubavitcher shochtim. Do you therefore reject meat from the major kashrus organizations and non-Lubavitcher meat producers that employ Lubavitcher shochtim? I guess you’d have to stick to Kiryas Yoel meat or Badatz Eida Chareidus.