I am completely against opinions in answers unless opinions were specifically and explicitly solicited...
...by the question, the clarifying comments by the author, or the text accompanying the question; in which specific cases, I'm totally fine with it.
When not specifically solicited, I feel that it detracts from the quality of the answer, is not factual, is not objective, is manipulative, and skews the site answers towards the emotional, and not in a beneficial way.
I recall several times across the stacks seeing a wrong answer selected because it was emotionally satisfying, or a factual answer bombed with downvotes due to unpopularity even though it was technically accurate, answers with a unique perspective bombed with downvotes because it was not mainstream, and I also recall seeing answers upvoted with large numbers, but a small vote answer was ultimately selected because it was more technically correct, and the other opinionated answers, while much more popular, were thereby less accurate.
It does highlight these unfortunate fact that "the right answers are NOT at the top" to paraphrase a quote.
In any case, I usually (but not always) downvote such answers as being inferior in quality as opinions detract from the value of the information, usually manage to come across as manipulative, dismissive, and spend more time proving their point than actually answering the question... and they frequently fail to consider the complete historical context of the game or component in question (this last is especially relevant to Dungeons and Dragons).
To be fair, there are a rare few I don't downvote, because I found the opinion interesting, or it opened my eyes to a new view or angle, or it was humorous. So that is a thing.
On the other hand, presenting facts about opinions is different, I feel. Noting that certain communities, especially subject matter experts, have found that certain combinations of rules result in given possible end results, or that a given point or rules combo is highly contested along with a brief, factual description of the debate without the opinion of the poster of the answer IS valuable information that allows the reader to make informed decisions.
(I am adding examples as I find them going forward. )
Supporting comment by another poster:
As mentioned in the comment by Interstellar Probe to this answer, and I paraphrase, "separating fact from belief is extremely difficult when researching a topic..." and this is true of this (and every stack) where high reputation individuals' opinions are often mistaken for facts.
Here is another example, by KRyan, no less, who strongly disagreed with my answer in the comments: https://rpg.stackexchange.com/a/166543/30200
At the time this answer was posted, it contained literally no reference to the actual D&D rules regarding diagonal movement, instead offering nothing but opinions.
How is that even considered a valid answer, when it doesn't even reference the rulebooks, or the existing rules on diagonal movement? This sort of answer is very non helpful, and detracts from the value of this site, in my opinion.
Please note this reference is not a slam on KRyan personally, who is very knowledgable, but a slam on both that specific answer as it was posted at the time I edited this question, and on the concept of opinionated answers in general.
I offer somewhat ironic thanks to KRyan for providing me with an example to support my answer here.
For the intent of preserving an example, and in compliance with the site (don't link, quote the info) concept, here is a copy of the answer:
As is common in D&D 3.5e, I am referring to “squares” when I really mean “cubes.” Just take “square” as game jargon, which it is in this case.
Anyway, so the “5-ft., 10-ft.” is an approximation of having diagonals cost \$1.5\times\$ the distance, which itself is an approximation of having them cost \$\sqrt{2}\times \approx 1.414\times\$ (Pythagorean theorem says a right angle with \$a\$ for the legs will have a hypotenuse of \$\sqrt{2}\times a\$).
A “double diagonal” will be the hypotenuse of a right angle with legs of \$a\$ and \$\sqrt{2}\times a\$, so the hypotenuse will be \$\sqrt{3}\times a\$, so we need an approximation of \$\sqrt{3}\times \approx 1.732\times\$. If we round that to \$1.75\times\$, we need “5-ft., 10-ft., 10-ft., 10-ft.” (so moving four squares costs 35 ft. of movement—\$1.75\times\$ the 20 ft. it would usually take.
Obviously, “5-ft., 10-ft., 10-ft., 10-ft.” is a pain, and also it’s much more questionable to start with 5 ft. on the first square than it was for the “5-ft., 10-ft.” scheme. It’s also less clear how to combine it with “single diagonal” movement in the same turn—you probably shouldn’t be able to go 5 ft. for a double diagonal square and then move on a single diagonal for another 5 ft.
The most accurate way to resolve this is to imagine the “5-ft., 10-ft.” rule as actually being “7.5-ft.” every time—then it’s really “7.5 feet (rounded to 5 feet), 15 feet (rounded to 15 feet, so 10 feet beyond the first).” For the double-diagonals, we’re looking at 8.75-ft, which is still rounded down to 5 feet the first time, and then 17.5 feet (rounded to 15 feet total distance), 26.25 feet (25 feet), 35 feet (35 feet).
Maybe easier to see in tabular form. Here, \$d\$ is the actual, unrounded distance, \$\lfloor d \rfloor\$ for the rounded distance, and \$\Delta \lfloor d \rfloor\$ for the cost of the latest step. Each step should cost what’s listed as \$\Delta \lfloor d \rfloor\$.
\begin{array}{c|c|c}
\textbf{Straight Line} & \textbf{Single Diagonal} & \textbf{Double Diagonal} \\
{
\begin{array}{c c c}
d & \lfloor d \rfloor & \Delta \lfloor d \rfloor \\ \hline
\phantom{0}5 & \phantom{0}5 & 5 \\
10 & 10 & 5 \\
15 & 15 & 5 \\
20 & 20 & 5 \\
\end{array}
}
&
{
\begin{array}{c c c}
d & \lfloor d \rfloor & \Delta \lfloor d \rfloor \\ \hline
\phantom{0}7.5 & \phantom{0}5 & \phantom{0}5 \\
15\phantom{.0} & 15 & 10 \\
22.5 & 20 & \phantom{0}5 \\
30\phantom{.0} & 30 & 10 \\
\end{array}
}
&
{
\begin{array}{c c c}
d & \lfloor d \rfloor & \Delta \lfloor d \rfloor \\ \hline
\phantom{0}8.75 & \phantom{0}5 & \phantom{0}5 \\
17.5\phantom{0} & 15 & 10 \\
26.25 & 25 & 10 \\
35\phantom{.00} & 35 & 10 \\
\end{array}
}
\end{array}
Combining single and double diagonals then becomes possible by leveraging those fractions—7.5-ft. + 8.75-ft. is 16.25 feet, so the second step when moving single-diagonal then double-diagonal is going to cost 10-ft, but the 1.25 feet “extra” is less than the 2.5 feet “extra” from two double-diagonal moves. By tracking that extra you can keep track of how far a character has actually moved.
And if you actually bother with this mess, I salute you, because this is insane. Unfortunately, yeah, this is the reality of 3D movement in D&D 3.5e. I strongly recommend a gentleman’s agreement to just keep things grounded, or houserule in some form of abstract flight—here’s mine.
This final comment, "... this is the reality of 3D movement in D&D 3.5" appears to be a statement of fact. This might cause a reader to consider this opinion to be a fact, and in fact, the rules of D&D.