We're not in Schengen because we're a sovereign nation who decided not to be in Schengen. In the future that will change and the EU will control 100% of our borders - they already control an awful lot of it.
So hang on, your argument for leaving the EU is not what the EU is now, or is likely to become in the foreseeable future, but what you fear may change at some point? I could make up any possible future to counter your argument but it'd be silly, wouldn't it?
Funny that isn't it? When a single market would be of advantage to British companies it doesn't happen. We've had to allow our service companies get bought by French nationalised industries, but when it comes to say, Scottish Power wanting to sell energy to France they aren't allowed to. At this rate we won't have any service companies left by the time they do introduce the single market for services.
It's a dog eat dog capitalist world, others have argued and won deals that benefit their people, our leaders for the most part have sulked in the corner. Even now it's not the UK government pushing for the single market in services but the very people you despise (the commission).
So now we have a prospect of a single market which will benefit not just the country but most likely every single one of us (by reducing bills in some areas) we choose to leave, we choose to not make any negotiations dependant on accelerating the single market proposals, and we moan about immigration - again.
That's cutting your nose off to spite your face.