You think you don’t, but you really do.You are probably thinking you don’t want to have to transition to a new key on some arbitrary date. But you can always extend the expiration later. And if you lose your key and don’t have a revocation certificate, the expiration date serves as a kind of “dead man’s switch”. If you don’t prevent it from being triggered by extending the date, your key will be automatically invalidated. This way, if you lose your key (and you don’t have a revocation certificate or have lost that, too), your key will not remain valid forever.
If you use Thunderbird with the Enigmail extension, per my previous tutorial, it is pretty easy to change your key’s expiration date from the Key Management interface. Right-click your key and select Change Expiration Date. Then you can select how many years, weeks, or days it should be until your key expires.
Of course, you will need to re-upload your public key so that your friends can get the extended expiration from the key server. Of course, you can also do the same with GnuPG from the command line, but I’ll leave that as an exercise to the reader.
And now you have no reason to have no expiration date on your keys!