If somebody votes for a party that you don't agree with, you're free to argue about it as much as you like. ... But on the other hand, if somebody says, 'I mustn't move a light switch on a Saturday,' you say, 'Fine, I respect that.'
First we thought the PC was a calculator. Then we found out how to turn numbers into letters with ASCII — and we thought it was a typewriter. Then we discovered graphics, and we thought it was a television. With the World Wide Web, we've realized it's a brochure.
Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so.
One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. There is no problem involved in becoming your own father or mother that a broadminded and well-adjusted family can't cope with.