Well those two sentiments come from similar sources. The vast majority of people that hear that Gambit's getting a movie, but are disappointed about not having Rogue in it are the 90s fans; the fans that started reading because of the show (small minority), and those who never read but love the X-Men because of the show (the vast majority). The small voices yelling in the crowd "he doesnt deserve a movie" stem from the same fans that didn't like that he was in the show over the likes of Iceman, Nightcrawler, Colossus, Dazzler and Kitty. They have younger acolytes that echo their sentiments, and sadly a few of these became writers who did their own thing, despite a lot of negative fan reaction (a lot of the more damning things they'd do to Gambit would be eventually fixed by the following writer or flat retconned by the editors). In the end it's all very small in terms of the amount of people that will ultimately see the film(s). All they do is piss off producers via cyber harassment, and spook studio types that put too much emphasis on the anonymous internet reaction. Take "Edge of Tomorrow" for example. It turned out to be one of the best movies of the year, but was nearly a financial failure due to preconceptions.
End of the day, its an X-Men movie with a recognizable character being played by an a-lister, directed by a man that has several franchise worthy hits under his belt. It'll be OK.
*I edited because of to some grammar issues and unclear thoughts. Sorry, my phone has a mind of its own and I sometimes possess clumsy thumbs!