Frankly,
I missed the option, and usually I am pretty good with noticing if the defaults are what I want. The only reason I even noticed that "delete" was not actually deleting mail was that I had to search through All Mail one day, and I noticed some messages that I was sure I deleted. What makes this worse is the completely counterintuitive nature of deleting messages from All Mail: they just come back. I suppose it should have occurred to me that this is a setting I can change, but considering the other oddities I have seen in GMail's IMAP support I just jumped to the assumption that it is another weird "feature."
Really though, the point still stands: Google was not considering protecting its users from government surveillance to be a priority here. They probably had other reasons, maybe even well-justified reasons, for the defaults they chose, but those reasons only make sense in the context of their engineering requirements.
"Also, I hope your email client does secure deletes on local disk by default."
I do something better: whole disk encryption. Actually, since I use an SSD now, "securely deleting" anything is non-trivial; it is better to just negate the need for it by never storing plaintexts anywhere.