Alright so I don't want to get into the overall idea of Marijuana legalization because I am for it. However I will share something from personal experience.
I work in the Marijuana industry manufacturing concentrates such as Wax and Oil for dispensaries in California. It isn't uncommon to hear someone tell you that's their profession if they are somewhat involved in the industry. However it is uncommon to find wax in a clinic that tastes/smokes like it's butane free. This is because these dispensaries give out ridiculous deadlines and don't allow manufacturers to completely purge their product. Personally there's a ton of manufacturers that don't bother to care about somebody's health. Many users don't bother to take note to the different taste when smoking Wax (oil) that still has butane in it.
The ingestion of butane can lead to many different side effects. Most common serious issue can be related to your immune system. Since most of the time a dab (hit of wax) is generally pretty small; you would only be ingesting a tiny amount of butane each hit. Similar to how beer tastes bad at the end, wax when your running low will contain more butane and gives off a much stronger taste if not whipped around. When only taking in small amounts of butane it is common to run into side effects such as dizziness, headaches, or shortness of breath.
However this is where it gets dangerous. If your a regular user and feel like you want to take a larger hit to get a bigger high, it may not only be that. Usually it would be alright to push yourself and it is possible to hit 1g of wax in 1 dab but that's with wax that has been purged correctly. Since anyone can get in this market there are many people out there that don't give a shit about anything but their product and the money. If your someone who tries to take a larger hit and the wax still has butane. It isn't uncommon for that shortness of breath to turn into asphyxiation.