I still believe that if my arguments for homosexuality are limited, then the onus is on you to explain why it is acceptable.
I will attempt to argue against your quote.
"Pleasure is good. Therefore, if we maximise it for all people, where is the danger?"
I believe that pleasure is a good thing to pursue. I am only against the VAIN prusuit of pleasure, which looks appealing in the short run, yet there are associated long term negative consequences.
I am assuming that you are athiest since you don't believe in the existence of God.
Take alcohol for example. It is very appealing. You can get drunk and have more fun at parties. It also makes you feel relaxed as it is a depressant. Recent studies have also shown that a glass of wine daily is very good for your heart. Indeed Alcohol is very pleasurable.
However, it is very obvious what the social, psycological and physical effects of alcohol can have on humans in the long run.
Alcohol has been associated with many car crashes where victims have been injured and killed and their families as a result go through trauma. Alcohol also kills brain cells and in turn is detrimental to your mental health. Also recent studies in New Zealand have proved that despite alcohol having some nutritious content, overall it is very dangerous to your health as it negatively affects other organs in your body including the liver and intestines. Clearly Alcohol is a vain pleasure indeed as there are many more disadvantages than advantages.
Also, gambling is pleasurable in the short run when you win a decent amount of money at the pokies. Yet it is also quite obvious what the long run impacts are, be it financial, social or physical. People become financially unstable because of gambling and thus become unable to pursue other forms of pleasure which are not detrimental to oneself. Gamblers arn't the only victims. Their families are also affected and there are known cases of suicide related to gambling problems.
Fornication is also a VAIN pursuit. Surely one cannot argue against the fact that sex before marriage is very pleasurable indeed. It is also healthy to engage in sex on a daily basis as it is beneficial to your heart. However, fornication destroys the social fabric of a society. Fornication, destroys the purpose of having an intimate relationship and love with only one person. Also, there have been many cases of unwanted pregnancy and most importantly the production of the AIDS virus due to multiple partners etc. Fornication is truly a VAIN pursuit of pleasure.
Everyone undoubtedly has sexual desires, and I believe that it is important to channel this desire through marraige to keep society clean and free from disease etc.