The Sudden Dawn of the Cosmos and the Constancy of Physical Laws

We don't.
Well, not absolutely, anyway.We trust them to remain constant because every time we get information suggesting if they were constant or not... that information suggests that, yes, they were constant.As long as that information stays that way, we will continue to trust such information.As soon as any information says otherwise, we will be become very, very interested in the how's and why's. A very good start.
And the start of all scientists.Now, let's look at what we can to see if they ever changed or not.
Everything we look at suggests that they never change.So, although the possibility of the Laws of Physics changing suggests we should not be confident in them never changing... the fact that we can verify that the Laws of Physics have never changed, and that we have no information that suggests otherwise... that is a good reason to assume that they'll never change.At least for now. Well, apart from the fact that it hasn't done so ever before. In all of it's 14 000 000 000+ years.
But hey... maybe tomorrow will be the difference maker?I don't know about you, but I'm sticking with the 14 000 000 000 years of not changing into an elephant.
If you want to side with the possibility of nave dreaming... that's up to you. Actually, if there is a Creator who established those Laws, this widens the possibility that such Laws may change.
Without a Creator... who would be able to change them? Maybe. But that sounds a lot like Atlas. I don't believe in Atlas or Jesus Christ, because all the information we have doesn't seem to back them up, only a very small specific subset. I'd have to ignore too much in order to accept them as truth. However, all the information we have does seem to back up the idea of the constant Laws of Physics.

I agree with your idea here, I think.
Your wording can be cause for some confusion, but I think I see what you're trying to say, and I agree. I don't agree with that, though.The word nothing implies, well... nothing.
Including not implying that nothing can come from it.Why can't something come from nothing? We have identified causes for many things. In fact, whenever we look for a cause, we almost always find one.
The only time we're really stumped for finding a cause, is at the very beginning of the universe.Since the very beginning of the universe only happened once, and only happened a very, very long time ago... perhaps our thoughts on what happens here and now (things like "something can't come from nothing") do not apply to what happened once, a very, very long time ago.Maybe. Maybe not.I can't say it does.
And you certainly can't say it doesn't. What's to say it's not going to?
Other than the last 14 000 000 000+ years of it not doing so, of course. Because it works.
Relying on the scientific method saves more lives than not relying on it.
Relying on the scientific method builds better computers than not relying on it.
Relying on the scientific method expands our knowledge about the universe and everything in it more than not relying on it.Maybe one day it won't.
Maybe one day something better will come along.
Maybe you'll be the one to identify that something-better.Maybe not.Until then, why not use what works? I don't think He does.
But this isn't exactly something to worry about, it's not as if I have a perfect track record of such things either.
In fact, pretty much nobody does.Interesting how God doesn't seem to be able to do any better than anyone else... maybe He isn't really a God.

By the best way of knowing. Testing and checking. I don't.
But we know they've never changed since we've been testing and checking for as far as we can test and check. Regardless of whether or not a Creator wants to change the laws of physics... if a Creator with the ability exists, then the possibility of those laws being changed is greater than if no Creator exists that can change the laws of physics.
For if no Creator exists that can change the laws of physics... who else could possibly change them? Heh.
That's like a child saying "You either give me candy or you don't love me!"
Naive and simplistic.Personally, though, I have faith in Love.The world is much more complicated and wonderous than you seem to want it to be.