As long as it's toggleable and completely an optional choice, I don't see any harm with wishing for the possibility to have reactions be automatic; Particularly if it helps speeding up the pacing of turns and thereby duration of combat. People enjoy and play for different reasons, there's not only hardcore D&D pen and paper players out there that are likely to play, but all sorts of players. Another, albeit off topic point of feedback, is that some people would like to just hide the dice roll on screen completely; It's not important to them.
So contrary to seeing it as taking away control from the player, I'd say having more options in how the game plays for you, gives more control to the player.
Well, so long as one of the conditions was "Any," than the player could choose to keep the pacing a bit quicker. For example, consider if the player could select Uncanny Dodge reaction to trigger (a) Never, (b) Any Attack, (c) Devastating Hit, (d) Killing Blow, or (e) CC Effect. The player could select "Any Attack" and forget about it. Another player, though, might wish to adjust these as needed, perhaps every turn.
