As a 4+ year vaper AND a former and lifelong habitual mxrijuana user, I think I can provide some insight here. Virtually NOBODY in vaping really hates on xxxx, and I find that most vapers either partake in mxrijuana in some way, or they're pretty positive when it comes to others who DO partake, and it's pretty obvious based on statistics that MANY non-mxrijuana users support the legalization and taxation.
The overall problem with the average vaper (whether they partake or not) lies in the assumption that vapers are "smoking xxx" out of these new high tech devices that are still FAR from mainstream. We all like to think that vaping IS mainstream, but it's still relatively unknown, save for a few dozen "hotbeds" in the nation. This means that WE have a responsibility as vapers to keep the two separate. Mxrijuana is still illegal in MOST states, and it has negative connotations because of this. Especially with the older crowd.
As a vapeshop owner, I would NEVER sell any devices related to mxrijuana. I'd say it's based on the legality, but I can honestly say that I would not sell these products even if we were in a recreational state, and that's largely due to those negative connotations. A LARGE section of the vaping customer base (especially in B&M shops) is in the 40+ crowd, and we personally have hundreds of customers in the 60+ range.
It looks bad enough when someone is in the shop REAKING like skunky xxxx when you're trying to setup a new customer, and it looks ESPECIALLY bad if the customer assumes that employees at the shop are the ones who are getting high. Many businesses don't drug test and couldn't care less if their employees are getting high, but they don't want these employees to be serving food or doing tax preparation while under the influence, and it's extremely bad for business if a customer thinks they are being served by someone who is high on the job.
In addition, if vapeshops DO sell mxrijuana vaporizers, we then get into an area where we have to have "off limit words" and we run the risk of setting up smokers with starter kits, while simultaneously having customers bringing products into the store that have residues from illegal products. Again, really bad for business.
I've also spoken to many people who have shifted from the "paraphernalia" industry, to the ecigarette industry (mainly glassblowers) and even though many of these people DO partake, they're still glad to be a part of a more legitimate industry...
I know this doesn't provide a full answer for why vapers are "anti-mxrijuana" but this does provide one perspective where it's clear that in certain circumstances, the association with mxrijuana can be bad for business, and thus bad for the industry.