You can use devices as cold wallet without having to sacrifice them, that was my point.
If you are no longer using the device as a cold wallet and have emptied all the wallets it was storing, then sure, you could put the WiFi card back in and connect it up to the internet again. You would have to start from scratch again in terms of airgapping and formatting the device if you wanted to use it as a cold wallet again though. You can't just reconnect and disconnect on a whim and think your device is still safe.
The goal of an air gapped computer/device is to be usable even if infected/compromised. You will never be 100% sure your computer is safe because nobody can guarantee that your operating system and the chips of your computer are free from any backdoor. It's ok to import datas in an air gapped computer, what is wrong is to send uncontrolled datas.