If the CEO of a gambling company said, "Gambling is good." Do you think that would be more or less effective propaganda that if the CEO paid someone else, let's say someone in a white lab coat, to say the same? I think that scientists are more likely to abuse the trust because it's implicit. You can't expect to abuse someone's trust in you (e.g. as a scientist) if you don't expect people to trust you. All the people you listed as untrustworthy are obviously untrustworthy, which is what makes them not a serious risk. Saying "I really want to trust scientists" is the same as saying "If you want to exploit me, use a scientist to do it." I don't think you need to look any further than the Tobacco industry to see why blindly trusting scientists is not a viable mitigation to propaganda.
I don't really have a good answer for how to make a good decision when you're ignorant (trusting scientists would make this easier), and we're all ignorant about most things. Being skeptical doesn't give you good knowledge, it just mitigates absorbing bad knowledge. So you're kinda stuck if you need to e.g. make a risk based decision about COVID and you don't trust scientists.