Taste is not opinion. Taste cannot be argued. Opinion can. The post which you say you will never be able to understand is taste. Your either mistake his post for opinion or you mistakenly believe that taste can be argued, hence you believe he did something wrong by posting "without really backing it up."
To show the person how his post looks to you, you attempt to state your preference for the older Fallouts in the same manner that he expresses his for the newer ones. You say, "I have way more fun with Black Isle's Fallout than I ever had with Bethesda's shoddy interpretation of Fallout," and your attempt fails. His post is taste alone. Your example is both taste and opinion. Had you had placed your period immediately after "Bethesda's," and had dropped the remainder, then you would have had it right.
When nu_clear_day tries to explain taste to you a few posts later, you reply, "And sure, you don't HAVE to frame your opinions, but you also don't have to post on message boards on the internet. If all you have to say is 'I like this' or 'I don't like that' then why even pretend to converse?" You further demonstrate that you do not know the difference between taste and opinion. You erroneously refer to "I like this" as an opinion, and you expect it to be framed as such, and you're just dead wrong to think it possible.
You are presuming to tell people that they ought to support their expressed preferences, yet you don't know how it is done.