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Are you thinking of "prejudiced"?

You might go with "closed-minded" or "small-minded" for the sense of not being interested in learning anything that might change their opinion, or perhaps "willfully ignorant" if you believe they've made a conscious decision not to educate themselves further about the matter.

I would describe what such a person is doing in that case as "speaking from ignorance" (in opposition to speaking from experience), but I can't come up with an existing word or phrase to describe someone as a person who routinely speaks from ignorance. To coin a phrase for it, I might go with "an oral flatulator."

Edit:

The speaker has a preconceived bias.

My answers:

• prejudice


• ignorance


• naïveté

I voted up prejudice, I think it fits. In your comments you stated you want to emphasize the fact the prejudice is uniformed. In that case, I think you could just qualify the prejudice:

• naive prejudice


• ignorant prejudice


• unfounded prejudice


• groundless prejudice


• uninformed prejudice

etc.

Pharisaical

Hypocritically self-righteous and
condemnatory.

Sanctimonious

Feigning piety or righteousness

As in A sanctimonious smug bastard

Self-righteous

Charlatan; fraud; counterfeit expert. My own invention is "instant expert: just add water!"

Poseur (poser).

Someone mentioned it in a comment, but I'll put it into an answer: the person is "speaking from preconceived notions".

Prejudiced is based on pre-judging, but I think it's not what you want. You can be, for example, racially prejudiced and yet have met people of the other race. The pre-judgement is not on a racial basis, but on an individual basis: you are judging an individual without having met that individual, based on what you perceive about the race to which they belong.

Another option that hasn't been mentioned -- but I also think it does not work in your situation -- is opinionated. Opinionated has the connotation of strong opinions not based on facts, but also does not imply this is because of a lack of exposure.

I would call that person a blowhard, possibly an ignorant blowhard if I didn't mind the arguable redundancy.

It's probably not what you are looking for, but confabulator is worth a mention. One who confabulates makes up incredibly detailed fantasies that they believe are entirely true, usually based on some very small piece of real information. For instance, you might show them a picture of sand and ask them to describe it. They'll start with sand and then tell you about the palm trees and the blue ocean, and the two people drinking Coronas under a rainbow colored umbrella. The important thing is that this is reality to them. It's a pretty interesting phenomenon.

ultracrepidarianism

the habit of giving opinions and advice on matters outside of one’s
knowledge or competence

You might say that person has an unfounded opinion. Baseless also works, as well as unsupported - although the last one is a bit more general, and could refer to lack of support from outside sources.

The term "armchair" is used a lot. An armchair critic gives opinions on subjects they haven't directly experienced. An armchair mechanic might say something won't work from a mathematical standpoint despite people doing it in their garages all the time. An armchair activist yells at the TV about how we all need to get up and do something about whatever political situation they don't like, but who never gets up to do anything themselves (this case also qualifies as hypocritical).

This isn't quite the same as your example though. In your example, you're talking about a purely subjective thing, while the use of "armchair" tends to be more objective. I'm not sure that "armchair pie-taster" works as well.

Of note, just because someone hasn't tried something doesn't mean they can't objectively determine that they would subjectively hate it. As an extreme example, I can be pretty confident that I would dislike getting shot with a gun without getting shot first. Similarly, I can use my experience in other fields of study to make a pretty good argument for a field of study I don't have experience with.

hubris

Merriam-Webster

exaggerated pride or self-confidence

"He exhibited a fair amount of hubris by ignoring his generals."

Jumping to conclusions


Example:

Jumper: "I have a strong opinion about X."

Clear thinker: "Can you give a definition of X?"

Jumper: "No. I've reached a conclusion without knowing the basics."