All religion is opinion.

[MineralMan]

15. That is true. Here's the Oxford English Dictionary's Entry

The key words in the first definition are "not necessarily based on fact or knowledge." One can have an opinion based on no information at all, false information, or without even thinking. However, it can also be based on solid, repeatable evidence, in which case it is far more reliable.

opinion
NOUN
1A view or judgement formed about something, not necessarily based on fact or knowledge.

‘that, in my opinion, is right’
‘the area's residents share vociferous opinions about the future’

1.1mass noun The beliefs or views of a group or majority of people.
‘the changing climate of opinion’

1.2 An estimation of the quality or worth of someone or something.
‘I had a higher opinion of myself than I deserved’

2A statement of advice by an expert on a professional matter.

‘if in doubt, get a second opinion’

2.1Law A barrister's advice on the merits of a case.
‘the solicitor took counsel's opinion’

2.2Law A formal statement of reasons for a judgement given.
‘a dissenting opinion adjudged that the government had the right to protect ‘the symbolic value of the flag’’