"Thou shalt not lie with mankind, as with womankind: it is abomination" (Leviticus 18:22). "If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them" (Leviticus 20:13)
Ah. Leviticus. Oh dear. First things first... Leviticus is in the Old Testament, not the New. As such it has little bearing on the Christian religion (beyond very interesting background reading; not that Leviticus is much use for that, but some books in it are really fascinating. Job for instance) in most respects... but I'll let you run with this as well.
This particular part of Leviticus (the worst written book of the Bible by far, but that is by the by) is taken out of all context more often than any part of any book ever written in the entire history of humanity (well... maybe not. But grant unto me the right for a little hyperbole).
First off, it is literally taken out of context. The acts described are part of a long list of various sins, generally of a sexual nature (although the first few aren't) and the recommended punishments are pretty brutal throughout (with execution being the favoured solution). Man lying as with woman is the fifth in the list of sexual sins. And it's not entirely sure what is meant by man-lying-with-another-man-as-wIt's actually lower than having sex with certain in-laws.
And it's not certain what lying-as-with-woman actually means, for several reasons. But that is also by the by.
Leviticus is a set of rules for a society that we do not live in anymore (unless you happen to live in a tight-knight nomadic society... which I doubt). And they are a set of, well more than rules, laws, which are no longer obeyed. Unless you live your life according to the book of Leviticus (if so that means no clothes made of mixed fibres, no pork and so on. Just thank the Lord that you aren't female; there's a lot of weird stuff on menstruation there. And plenty of ever useful information about how to sacrifice a goat) then you really have no right to complain that others don't... and here's the thing. There is no requirement for Christians to follow the laws in the book of Leviticus.