Sure, but you missed my entire point, which was we don't want to contaminate the samples.
The entire point is looking for evidence of life and organic material. Would be a shame to spend all those billions just to not be sure if the organic material we're looking at came from Earth or Mars.
The onerous requirements have nothing to do with protecting the samples in their sealed containers; the issue is overblown fear of contaminants on the _outside_ of the containers reaching Earth, It's comparatively easy to seal a container remotely, before it leaves the surface, compared to the task of sanitizing it against all hypothetical threats while in transit.
No one's arguing against protecting the samples from exposure to Earth life; the contention is to what extent we need to "protect Earth life" from the cooties hitchhiking on the sample return system.
Wouldn’t we be able to tell under an electron microscope?
Short answer: No.
Long answer: Maybe, but it would take a lot of detailed study to be absolutely sure.