virtualisation and multi-threading have both been regarded as security risks since their inception.
Regarding virtualization, I can't remember anyone running around telling people "don't use this!". These kind of ideas need time to ripe, the CPUs need to become faster, the systems more complex & optimized until a problems pops up. Hell virtualization started with IBM's VM series in the 70s. It's been a long time. When did the first warning surface?
Now for multi-threading I have found a Hyper-Threading Considered Harmful from 2004, so this point is well taken.
Biting the hand that feeds IT
