What would happen if some bad people launch 1 million transactions in 1 click? Would the cost be only ~2-5 millions usd ?
I'm trying to understand your question, are you asking if a rush of transactions would slow down the network and lead to higher fees?
What's the $2.5 million in this scenario?
Second question in case question 1 does hurts why bad people don't do it right now?
What would be the purpose of this? To slow down the network and expose shortcomings in bitcoin?
Lagging is a normal effect of a sharp increase in number of data processed over a period of time.
PS: I'm talking about really nicely made transactions that look like normal transactions and couldn't really be distinguishable from the rest of the transactions appart from the fact they would have the same ~timestamp.
And we could also think about a slow attack spread over time.
AFAIK, Timestamp are attached to blocks and not individual transactions, so the time you broadcasted the transaction does not really matter.