Do you not think that a major government initiative in HSR (which it would require, tax dollars or not) wouldn't come with the standard TSA security theater in tow?
Probably not -- they know full well that people take trains to avoid the TSA and that they would have substantially reduced ticket revenue if they put people through that nonsense.
I think there will certainly be a measure of security with such a system, but it wouldn't need to be at the level of air travel. The danger of someone hijacking a train is finite - it has a definite path and that pathway can be planned to avoid Problem X or Problem Y. That's very unlike a commercial jet.