First, you don't know that population trends will continue, or that as you seem to suggest, reflect proportion of Muslims changing at an exponential rate (and if so, that they will continue to do so). Second, even if the population eventually became 100% Muslim (which might take 250 years, but w/e), they'd still only have ~40% support for Sharia Law (assuming things stay the same).
With all due respect, what utter bollocks.

Islamic families have like twice as many children as non-Islamic. Yes I pulled that number out of my arse, but it's probably about right. That isn't going to change, white families don't tend to have the desire to have six children. So their population will continue to grow.

Also, if Sharia law doesn't happen even if we hit 100%, then how do you explain Sharia Law in Islamic countries? I can only assume the Islamic population is approximately 250% of the overall population.

So the Sharia Law freakout argument is obviously bogus.
If by "obviously", you mean "in my naive opinion", then you're bang on here.

You clearly have some other reason for not wanting them here.
Incorrect assumption. I haven't got a problem with Buddhists, Hindus and Sikhs.

Maybe because you're not comfortable around them for whatever reason.
There's an Islamic girl, hijab included, who sells the Big Issue outside Oxfam. I make her tea and make conversation with her. She's nice. So that shows what you know.

But don't try to argue stuff is going to happen that isn't.
You hope. I hope I'm wrong too.