You say "the only question is do you support cruelty toward animals or not?" The point of what I'm trying to say is that this is not the only question. I, for example, strongly oppose cruelty toward humans. Nevertheless, I would not favor launching a full-scale nuclear war to wipe out the entire human race, even though this would drastically decrease the quantity of cruelty that human beings will endure over the entire course of history.
The aim of preventing cruelty only makes sense if we believe that life has some value, otherwise the simplest way to prevent cruelty will just be to have no life at all.
[…]
People eat cows because beef is tasty. The question is whether or not this is morally problematic. You say that it is problematic because in order to eat beef you have to kill the cow and treat it cruelly in a variety of other ways. I am suggesting that veganism, too, is morally problematic because its adoption would de facto eliminate cruelty to cows not by eliminating the cruelty but by eliminating the cows. It seems to me that if you consider the possibility of eliminating cruelty toward humans by eliminating humanity you will see that this is absurd.

Scientists in Pennsylvania yesterday said they had turned ordinary mouse embryo cells into egg cells in laboratory dishes -- an advance that opens the door to creating "designer" eggs from scratch and, if repeated with human cells, could blur the biological line between fathers and mothers.

The work undermines the standard model of parenthood because the scientists made egg cells not only from female cells, but also from male cells, indicating that even males have the biological capacity to make eggs.

If the science holds true in humans as in mice -- and several scientists said they suspect it will -- then a gay male couple might, before long, be able to produce children through sexual reproduction, with one man contributing sperm and the other fresh eggs bearing his own genes.

[. . .]

Until now, one argument for banning the creation of cloned embryos has been that it would require a huge supply of human eggs to make all the embryos and therapeutic cells that patients might need. That market demand could lead to an "egg-donor underclass" of poor women who might submit to repeated, health-compromising egg donation procedures as a way of making money.

But if scientists can grow lots of human eggs in the laboratory, experts said, that market would not appear. "Commodification and safety issues would be avoided," said Judy Norsigian, executive director of the Boston Women's Health Book Collective, who has been a leader in the movement against what is known as therapeutic cloning because of the risks it might pose to poor women.

[. . .]

Perhaps most astonishing, said Eppig of the Jackson Laboratory, the lab-reared egg and follicle cells apparently engaged in the complicated cross-talk required for normal development. Follicle cells surrounded each egg in a gentle embrace as they would in an ovary, for example, and even produced female hormones, which the eggs need to mature.

"I am flabbergasted that these darn things are making estrogen," Eppig said. "Imagine what's going to happen when you can do the same thing and make sperm."

The genetic program for making sperm is believed to be more complicated than for making eggs, but sperm farming may not be farfetched, Schoeler said. Success could raise interesting questions about the biological relevance of males.

If sperm can be made from stem cells, for example, then lesbians could make babies by sexual reproduction. Unlike gay men, they would not have to turn to the other sex to gestate those babies.

"It will take a nanosecond for people in same-sex relationships to figure out the potential implications of this research for them," said Murray, of the Hastings Center. "People can just fill in the blanks."