Next time you go into an argument

try to show us why a certain position is invalid without mentioning or guessing at the motive of the person.

This can be done with any argument. In fact, mentioning what you think the person's motive is for believing a certain thing will not help your case at all. You cannot disprove any claim that way. You cannot even prove bias that way.

If they use statistics or mention scientific studies to support their argument, you have to find the source of those to determine whether it is valid. If the person does not state his source, then it does not support his argument.

Those who attack a person's motive are the ones that are truely incapable of being objective.