They've got "a connection to a dark force" based on their creator deity being evil, but caution is the way... and yet with tieflings I think your bias (liking tieflings) is showing...
Tieflings are simply more common because they're human-adjacent.
I have no pro-tiefling bias. I have no anti-tiefling bias.
The only race toward which I am biased is
dragonborn.
Uh, Tieflings are LITERALLY descended from demons or humans transformed by Asmodeus (unless something has changed recently and I missed it).
Notice how you already had to add an exception ("or transformed..."),
and it's now descent, not just direct creator attention.
All minotaurs were either directly created by Baphomet (IIRC?), or can trace direct ancestry to such.
All of them.
There is no "my great-grandfather accepted a contract he shouldn't have, so all of his children were born with horns" thing, where the children did literally nothing wrong and were merely infected by one or more parental misdeeds. There is an inherent separation, even right at the beginning. Consider people like Wyll from BG3, who becomes functionally a tiefling because he was
cursed. Where's the evil there? There
isn't any. It's nefarious
manipulation.
That's the key difference. Perhaps, to you, it doesn't matter. Certainly
to me it doesn't matter, and in the actual game I run--and any other game I might run, other than one with a heavily-established setting where racism is explicitly included and extremely strong, e.g. Dark Sun--I don't
do racism. Like, at all. Racism is almost completely
boring as a fantasy moral trope because it has only three outcomes: the bigots are bigots and the victims are laudable; the bigots are right and the victims are evil; or the bigots are bigots
and the victims are evil. None of those outcomes even remotely interests me, so I simply don't use racism as a setting conceit. I use it--extraordinarily rarely--as an individual character trait when I want to make a particularly hate-worthy character, and that's about it.
Isn't either explanation... literally a direct connection to a dark force (by blood or by literally being magically transformed by an incarnation of Evil), too?
As stated above: No, because sometimes it's indirect. Other times, it's a transformation unjustly inflicted on someone who literally never did anything wrong in their whole life.
Shouldn't "caution" be advised for the same reasons rather than "there isn't that much to fear"?
Well, there's one other significant element there. Minotaurs are a hell of a lot
bigger than tieflings.
They seem to me to have a much "closer" connection to evil than minotaurs since they owe their very existence to the physical incarnation of evil itself (either in outsider lineage or Asmodeus’ direct intervention).
Why? To me it's almost guaranteed to be a much, much,
much more distant one. Because, as stated, 100% of minotaurs come from beings directly,
personally created and taught by Baphomet(?). The vast majority of tieflings don't have that connection. It could, quite literally, be that their great-grandfather did a bad thing exactly once, and the curse has only finally flowered three generations later, in a child who literally never did anything wrong and who came from parents who literally could not possibly have known any of this.
Further, all the lore I've ever seen about minotaurs explicitly and specifically indicates that they retain a personal connection directly to Baphomet. Those who choose not to be like the stereotypical minotaurs work very hard to limit or cut off that connection, but (again to the best of my knowledge) it is 100%
always there, lingering, waiting for a moment of weakness. Nothing of the sort has ever been true of tieflings, or indeed even of other sorts of things.
Remember: All you need to be a tiefling is that one of your ancestors, at some point in the ancient past, was
some kind of fiend. Has nothing to do with direct creation by Asmodeus.
Any human with even the tiniest drop of blood connecting them to a fiend, or the curse of any fiend, or even just an act of great fiendish magic which an ancestor happened to be witness to or target thereof, can thus be born a tiefling. The connection can be as remote as a dozen generations or as direct as "I was personally cursed to be a tiefling."