As someone who lives around these parks, I'd like to make a few comments to give some needed illumination on the subject. The media's using this for cheap shots, and it's more serious than that:
One. The serious maintenance deficit started under GWB. Obama and his Congressional opponents did little to nothing to alleviate the significant issues. It's been a political football lobbed to future Administrations by Presidents of both parties much as North Korea has. Trump is in the position now of having to clean up the mess, because it won't wait any longer.
Two. Parks, partly thanks to social media, are being 'loved to death.' And the significant increase via social media happened after the problem already existed. It's been a disaster, really. Too many people ruin the experience of the outdoors, and pound the facilities to a pulp. Remember the outcry in '07 and '13 when Yosemite proposed limiting visitors. Yet popularity turns these places into mall parking lots ... places that should never see half that many vehicles. Price is one way to control popularity. NOT my preferred method, certainly, but one that makes sense given #1 above.
Three. The current Congress ain't shelling out for the NPS. If anyone believes so, I've got swampland in Florida for sale.
Four. The facilities are worn, often ill-functioning and dangerous. The boardwalks at some Yellowstone geyser basins are flat-out life-threatening. Besides having clueless social/selfie takers walking out on the thin crusts, railings are not even able to support the weight of a large child. A kid fell through and was burned when I was there in '05; according to a ranger, the second one that day. Many areas with bad/rotten wood on the platforms. Such small incidents never make the local papers. The NPS quietly puts up with all this. The NPS was never designed for being a police department, EMTs, but they now hire significant numbers of law-enforcement and first-aid trained personnel. What happened to the "Ranger"? Too many people doing damn fool things for them to have time to point out flora and fauna. Without proper walkways, railings, safety anchors ... well, you can imagine their current overwork, given that with the deficits in their budget, they cannot hire enough people to guarantee safety.
Five. $70 is less than the cost of two people going out for a dinner at a modestly-priced restaurant in downtown Santa Fe. If a family of four can shoot over $100 in one night on one meal ... how expensive is $70? We see families of all economic levels enjoying the restaurants here. Take two adults and two kids to a two hour movie in Santa Fe [The Last Jedi, Violet Crown Cinema], you spend $42 - without munchies - I suspect popcorn, overpriced candy, giant sodas can drive that up closer. Point is, yes, it's double the previous price. But that price isn't so far out of a single-day outing for a family, is it? But is it worth it? Damn straight it is. Even more, when you realize where the money's going (from my understanding, the arrangement is that the majority stays in-park).
All in all, we're caught between a rock and a hard place. The parks NEED maintenance. The Feds haven't, aren't and won't be doing it. NPS HAS TO DO SOMETHING. They've been on the ropes for over ten years now, and nobody's given a damn. For some parks, if they don't get money, they'll have to close down some popular locations.
Later, important Addendum: The NPS themselves say that of the ticket increases, 80% will stay in-park.
(I wrote this originally on Hal Rager's FB timeline, in answer to a specific link. Reposted here, with a couple of mild edits, because I continue to see people screaming and yelling with no real knowledge of the subject in the news media.)