There's a value to things like brands. Obviously, because we will buy things adorned with brands that we know, recognise and trust. Therefore they are valuable to their owners and they strive mightily to protect that value by making sure that the brand and products adorned with it can be trusted. This thus is a very odd complaint:

Doctors warn of big tobacco firms entering e-cigarette market

Royal College of Physicians report says companies may seek to rehabilitate ‘pariah industry’

Well, yes, the replacement of a product that please people but kills them with something that pleases them but does not kill them would appear to us to be a pretty good method of rehabilitation.

But there's a larger point here too. We positively desire those large companies, with their brand names to protect, to be in this market. For their own self-policing will lead to consumer protection. We would illustrate this with reference to the heroin market.

Imagine that we all did the sensible thing and just legalised the stuff. No, not just decriminalised it, made it simply legal. there would then be companies using those standard branding techniques (there are already illegal dealers who do this on a modest scale) to reassure users. Of the purity, dose size, absence of talcum powder ans so on in the formulations. For example, the biggest cause of opiate overdoses in the US these days seems to be the cutting of heroin in fentanyl, another opiate. One with a very much smaller margin between bliss and death unfortunately. A known and legal brand would not survive such cutting and contamination: thus a known and legal brand would not allow it to happen.

And so it is and will be in the vaping market. The economics do not change because of the legal status. Large companies moving into the market with their brands to protect will lead to greater consumer protection over quality issues. That's what brands are, what brands do.

We don't want to be concerned about the giants moving into this territory, we want to encourage them.