For too long, "rider bills" have been used to sneak in "extra" legislation which holds no merit or is controversial. While proponents of "rider bills" advocate that it's a way of "getting things done", it wastes time and prevents legislation from getting passed. Democrats have done this, but most recently, it was the GOP. The GOP previously did not support Zika funding. At the time I write this, they have attached to a Zika virus funding Bill, provisions related to gun rights, abortion, and gay rights. Now they play politics, to make Dems look bad for rejecting the Bill, and they immediately accuse Democrats of "partisan politics", "playing games", and "blaming GOP".
A Constitutional amendment must be passed to ensure that Bill provisions are directly related to the summary in the Bill.