I don't think that is very ethical. I think it is better to ask someone to guest you in than steal your way in.
Neither method is terribly ethical.
But let me ask you this, what if you pay the $450 for the AMEX for the year and get the 25K miles and close it after the year.
Is it wrong to use it then? Does it say somewhere that once you cancel the card you're not allowed to access the lounges? No. All it say is that with the card you can access lounges (at least until the card's 4 year expiration date.
Definitely no possibility of C"H as nobody even knows its canceled as opposed to panhandling at the entrance of the lounge for free entry which is likely to offend many people.
Personally I enjoy lounges enough to have invested in a lifetime membership years ago, but for everyone else they'll have to decide for themselves...