Civillians spawn outside of the map. It's not a matter of paying attention or not.

Here's the official post about Overkill's stance on modding:

Here's the rule: use common sense. Are you screwing up the game for others? Don't do it. Are you blatantly cheating to gain things in an instant that otherwise would take a lot of time? Don't do it. Are you having fun with your mates, they're having fun with you and everyone's in on it? Go ahead. Enjoy yourself. It's a video game after all.
What about my game changing mod?
So your mod changes the game in a huge way? Sure that's totally fine however as Almir has stated, do what you can to prevent ruining the game for other players. If we feel your mod might ruin the game for others we will delete it from the forum.
What can i do to avoid any issues?
The best way is simply inform other players you're using a mod. Adding an automatic message to your mod that informs other players you are using a mod will pretty much keep you safe from any other problems. If you're making something easier, try to balance it out in some way. You can also make it so the mod can only be turned on in friend only lobbies.
What goes too far?
Anything that can cause other players to have less fun will be removed. This also includes mods that make the game significantly easier just to unlock achievements. Anything that lets you unlock something without putting any effort in won't be allowed. Use common sense and you'll have no problems!
Provide credit when due!
A lot of modders work very hard to make the mods that many of us enjoy. If you create a mod that used parts from another mod please provide credit. Anyone who does not provide credit and is not the author may get a ban. Nobody likes having their work stolen!

Does removing invisible walls somehow gain everything in an instant? Does it ruin other people's fun? No, and it depends on the person, but in most instances, no.