Guys like Sangakkara and Lord Saint Prince Buzz McCellum often only wore the gloves because they were the best option at the time.
No these two were genuine keepers. McCullum quit keeping supposedly because of back injuries and wanting to focus on his batting. Sanga, like Tilikiratne before him also wanted to focus on batting but he is very much a genuine a keeper.
Alec Stewart however just did as he was told, if he was the best option or not

Same with Wayne Phillips. Interestingly BJ Watling only took up the gloves after a failed test career as a batsman specialist, to earn a way back into the NZ team (if cricket mattered in NZ this would be a bigger story than Beaver white baiting). Despite not being a keeper beyond age group previously bar his very first two FC games, he seems very good with the gloves, not Dhoni stumping good, but far more than adequate - esp when combined with his batting. He saw an opportunity post McCullum quitting gloves and he went for it. Legend.
http://www.stuff.co.nz/sport/cricket/6272377/BJ-Watling-steps-up-his-wicket-keeping-ambitions
de Villiers is the one with the amazing batting record as designated keeper as 'best option" - 57 vs 49 career without gloves - but he is an anomaly. A natural keeper as well, he loathed the extra work rate and wanted to focus on batting and captaincy, not glove work. But he still did it when say QdK was injured.
Bairstow and Buttler are equal with Bairstow atm the better test batsman who could fill their 3 spot.
Apparently, Ben Foakes is the best wicket keeper of the lot easily. But Buttler made runs in the IPL so got a chance over him.
I agree with JJ and the rest of many, it does seem different for Johnny to want to keep the gloves when the team has Buttler at 7 and him at 5, and could possibly benefit from him moving even higher. I get that Bairstow may want to keep his position int he team guaranteed, I think we can respect that he wants to keep representing England and earning big bucks, but this is an indictment on not having faith in the selectors to put back down in the middle with the gloves if it goes pear shaped up the top without the gloves. But as a player, would you have all that much faith in selectors as you watch more and more cricket?
I think its far less a confidence of performance thing and far more a confidence of keeping his job thing, and far more Johnny wants to keep earning millions of pounds each year, and by keeping the gloves, he will prevent the selectors from stuffing him over. He doesn't want give Buttler or Foakes a sniff at the job he has made his own. And I get this.
The selectors need to tell him what's what. Players who are not captain should be not be dictating terms to them at the highest rep level - it isn't like Johnny can just switch teams without an intl stand down. Selectors should be doing what is best for the England team, not for Johnny.