Yes and yes. Even on its own, vaginal secretion is an acidic sperm killer that repels healthy sperm before it can enter the cervix. Store-bought lubricant only slows the sperm further, leaving it more likely to die within the vagina, before reaching the egg.
Need an alternative? Try Pre~Seed, a new lubricant that's advertised as "fertility friendly," and doesn't seem to harm sperm. Or, try a home remedy. Some couples find water or even egg whites works as a non-toxic lubricant. There's also the old-fashioned option — save your money, step up the foreplay and let nature do the rest.