I think I'm in favor of them. Maybe it'd be different if they came at the expense of entirely new games, but I don't think that's the case, even with the updates these Switch ports sometimes get. This goes for both Nintendo and third parties.
Nintendo ported over a couple of Wii U games thus far, but these were either games that couldn't do well on just the Wii U (Zelda and Pokken) or simply benefitted that much from a new version (MK8's joycon controls and Battle mode). I've noticed that games like Super Mario Maker, though popular on Wii U, weren't brought to Switch, which is a worse fit for the game.
As for the ports of older games from third parties, most of them are finding a relatively new home. Skyrim, LA Noire, Dragon Ball Xenoverse, and Rocket League have never been on a Nintendo platform or on a handheld. The biggest exception to this seems to be Rayman Legends, but Ubisoft loves porting Rayman games anyway.
