Tony Verhulst wrote
...Nearly outlanded at a Class-D field, and would have had to
outland if I couldn't have communicated with tower ......

No. There are procedures to deal with that situation. See the Airman
Information Manual and FAR 91.129(d). Hint: know your light gun signals.

I know my light gun signals. Light gun signals and the appropriate
responses are considered communication with ATC. So as a private
pilot, I could enter the Class D surface area without a radio.

This option is not open to the sport pilot; the issue is not lack of a
radio but lack of operating privileges in airspace requiring
communication with ATC. The sport pilot will not be required to know
light gun signals either.

Michael