If they don't have an order, they should not come in (unless invited to do so, of course). It has nothing to do with being "suspicious."

I fully agree. But you're saying that while commenting the situation from a distance. If it actually happened to you you might react differently.

(If there is a number of guys with guns at my front door I'd probably have to let them in..)

From a distance and another country. I don't know what I'd do in the situation, but at least I'd ask if they had it... So I could use the fact later

Or let them in to find bomb making material that's in every modern house and get sent to gitmo. Tough choice..

It doesn't actually make you suspicious, it just indicates that you're an informed citizen. If you paid attention in 8th grade civics class, you'll know that you get to ask if they have a warrant.

Reading the warrant will give you some indication of what they're interested in. If they don't have a warrant, then you can decide if you think you should let them in.

It's up to you; if I'm on a jury, I won't find you more suspicious if you question the police before allowing them into your home. I'd guess that there are other people like me.

My situation is actually even easier: I did not have 8th grade civics class as I'm German and live in Germany. While the government/police (to keep in power) wants us to believe that there are terrorists, I actually feel very safe living in a district with a very high muslim population. [0]

We just don't have that much police and secret services poking around in our private lives (yet), so let's see what I'll do when I actually come into the situation. :)

[0] https://en.wikipedia.org/wiki/Berlin_population_statistics#P...