A tongue isn't neccessary to survival and yet we would call someone who went out ripping people's tongues human rights violators among other things. Not being neccessary is not sufficient to for something to not be a human rights violation.

I wouldn't call speculation in itself a human right but it emerges from others like right to trade and ownership. Taxing unoccupied homes would be a way to address it perfectly respectful of human rights - fixed costs of infastructure upkeep need to be paid after all.