Even if you think 'the will of the people' is anything other than a slogan, the fact remains that at best the 'will' is simply to leave the EU.
The lack of understanding about what this entails has been demonstrated time and time again, none more so than this week when some people thought the ruling meant Brexit was over.
There is no mandate for how we leave which is why it must be debated.
Those who's priority is immigration just happened to have been happy with that going unchallenged and are now angry because they know it won't now be allowed to be so.