You give a list of practical ramifications of laws regarding sexual behavior, then you label them as "fundamentally wrong." Historically in law all the things you mentioned have been considered wrong, not for practical reasons (as you list) but since they are "fundamentally wrong...." and as soon as morality...i.e. "wrong" is mentioned religious issues (even if tangental) come up.
Rape for example, is accepted in some societies today (and has been in many in the past)...with a kind of "boys will be boys" mentality. Incest was the way Egyptian Pharoahs were raised...(and a minority of those born to incest have genetic problems...though it is a SIGNIFICANT minority)...so in some cultures incest has been accepted. Beastiality has been accepted, in various times and cultures--as most all societies don't give a rip about animal "consent"(does your dog consent to that fence or leash?) and again it was seen as an outlet for the oversexed.... (gross, definitely.) The point is, in the history of our law, moral, not practical, bases were the reasons why those three deviant behaviors were (and are) outlawed. Homosexual behavior too, has been proscribed due to moral (and yes, religious) reasons.
Our very concept of human rights is based on those "endowed by the Creator" to quote Jefferson in the Declaration. Do you really think America has been a theocracy until the ACLU flexed its muscles???
Back to the specific issue however at the same time, without resorting to the religous, many practical reasons can be found to restrict homosexual behavior. These include, obviously, the spread of disease (since homosexual men by any measure are persistantly VERY promiscuous) (AIDS didn't spread through heterosexual monogamy now, did it?) Homosexual relationships tend to be more violence prone.... Homosexuals have a MUCH higher than average tendancy to molest children. (something like 1/3 to 1/2 of reported child molestations are homosexual....by a group which is less than 3%....you do the math). Finally, homosexuals do nothing to promote healthy interaction between the sexes--including the production of children. These are all practical (and yes arguable...as is your list, to some) reasons why homosexual behavior is not a good thing...but wait, there's that pesky word "good" which relates to values, which, ultimately must relate to religion...and has done so historically in our society and law, as in all others.
The acceptance of homosexual behavior or not, is not about the religous, vs. the practical or non-religous--its about one religious/value system vs. another... Secularism is as much a religion as the most backwoods bible thumper. Since it pretends not to be, to my way of thinking--it has even less tolerance.