A "mainstream" person can also consider past evidence of A, B and C doing Y and assume that X is doing Y too without any evidence about Y.
A "mainstream" person can also consider past evidence of A, B and C doing Y and assume that X is doing Y too without any evidence about Y.
"Mainstream" people will also look at past evidence that A, B and C did Y, and say something like "that was N years ago, surely nobody would do this today".