Okay, I did a poor job of explaining my reasoning in my original post, and I apologize for that.
I actually have no problem with mesmers using portals in JPs normally, only with a JP that is a daily. This is for two reasons. When you do a JP normally (when it’s not a daily), you get a chest at the end, and an achievement if you haven’t done it yet. When you do a JP for a daily, you get the chest at the end, the achievement if you haven’t done it yet, progress towards Daily Completion, and a Chest of the Athlete. The rewards are greater when a JP is a daily.
Even more importantly though, when you do a JP that is not a daily, you won’t find many others doing it with you, if there is anyone else at all. So unless you get lucky and a friendly mesmer happens to be doing it at the same time, you’ll probably have to do the puzzle yourself, or find someone willing to help you (guildie, friend, someone in map chat, etc.) When a JP is a daily, your chances of finding a mesmer already there to port you are far, far higher.
I don’t care if mesmers port people in a JP that is not a daily. If you’re able to find one to help you out, go for it. But there’s a difference between one person struggling to find a mesmer to help them and receiving 1-2 rewards for it, and groups of people getting ported for 3-4 rewards.
But as I said in my original post, I don’t believe removing mesmers’ ability to use portals in JPs is the answer. If the devs did this for all JPs, even if they’re not the daily, this would punish innocent players who may not like them, or have trouble doing them (I thought about mentioning this in my original post, but felt it had been covered by enough people in the thread already). But even if the devs were to implement a way to disable portals in a JP only if it is the daily, this is the wrong way to go about it. It punishes innocent players as well as the lazy ones. And yes, in addition, this kind of solution would require quite a bit of work for the devs. The best solution is to simply remove JPs from the daily rotation. That way, people such as myself and Wisdom don’t have to worry about lazy players being rewarded, people who dislike JPs or have trouble with them no longer have to worry about seeing them pop up in their daily lists, people who enjoy JPs don’t have to worry about doing one for a daily and finding it much harder to complete because of the multitude of people making it harder to see things or creating lag, and it’s less work for Anet. This feels like a win-win-win-win to me.