I have to say, I'm with the "capture is fine" crowd. So long as your setup isn't pure fiat, I see no problem. It's a staple of many fictional stories, and it makes for a great story for the players to tell in later years.
In my current campaign of 13 years, I've captured one or more of the PCs on number of occasions, only making sure that in various lone captures not to repeatedly focus on a single PC. I have never had a player personally mad at me for laying a trap that neither they, nor their character with all their skills saw coming despite hints, rumors and clues. Nor have I ever had a player mad at having lost to an enemy group that used better tactics or teamwork than the PCs, whether capture was the initial intent or not.
I've captured the priestess of a party with a debonair villain, only to have the party try to rescue her, and get captured, only to have one escape, hire allies, and stage a counter attack, which freed the still captured PCs and gave them the opportunity to get in on the fight and shatter the evil priesthood that had them.
I've had them lose a more or less frontal assault against a slaver compound, and the PCs who got away purchased their friends back rather than engage again, still having succeeded at their primary goal of freeing other slaves in the initial assault.
In those instances where only part of the party was captured, I've either flipped back and forth between the free and captured PCs playing out their various scenes and interactions, or allowed players to play henchmen or hirelings who were aiding in the rescue attempt, or even dopplegangers or transmuters infiltrating the party after getting the first to lure the others into capture.
Don't get me wrong, it's lots of work for the GM, especially keeping everyone engaged if they are separated, but in my opinion it's not a show stopper. And I've never had angry players, though I did once have a player who argued that they were bleeding out, and should be dead. Until it was pointed out that smart slavers keep a couple priests of tyranny on hand so their product is always in good condition.
In the end, as SPoD, Shilsen, and others have said, if the encounter makes sense and is built with and executed with the rules...quality players will play with the story.
If you use the Fiat Locomotive, and arbitrary superceding of rules, you'll get mad people.
As for actually doing it...how much prep/intent does this group have with regards to the group? Ie, is it more along the lines that the PCs stumble into an encounter, and the enemies' natural inclination is to capture on the fly; or is this group intent on specifically capturing this group of heroes for some reason, and willing to expend investigative time/energy to ID the best way to engage the PCs to capture; or are they just generally slavers/brutes who will capture anyone who travels the specific road? As that will likely help you define how specialized the captors will be in their attack.
PS: I've never specifically warned my players or asked their permission to have their characters captured prior to an encounter. And that actually makes no real sense to me. On the other hand, the campaign was prefaced with "You may run into things wandering the world that you cannot reasonably defeat at any given point, but may be able to handle with planning, investigation or advancement. Logical conclusions and consequences will follow actions taken." I think it's thus more imperative that the ground rules for verisimilitude and consequence have been laid out for the run/campaign as a whole.