Woah. I see something inflammatory and probably hurting the feelings of someone sitting on a computer somewhere.
Therefore I must add my two cents.
This isn't entirely well thought out, so it may need some translating, but:
1. Gay.
So far through research and trial-and-error we have ascertained that a person's sexual orientation is usually genetically caused, and is usually not affected by upbringing and how much the parents wants them to be gay or not.
Likewise, being in a gay relationship does not seem to be harmful or psychologically damaging to either of the participants, except for the larger incidences of blood borne diseases amongst male homosexual partners. This has been combated with some pretty rigorous sex-ed, but only in certain countries or states.
So, whilst homosexuality in some places could be bad for people, in today's society it is becoming less so.
2. Violent relationships.
This is a tricky one. The BDSM community often has their share of masochistic and sadistic people, however these people are actually rather rare. Most of the community is just about power play and emotional interactions. The Dom feels powerful and like a provider, which makes them happier in the relationship, and the Submissive (strangely enough) feels safe and trusting, which makes them happy. That's the normal reaction of that community. One person completely trusts another, and through letting go of their own inhibitions, they both get their kinks. However, people who have the pain-pleasure transfer like masochists are not as common.
And that's where this stuff all gets tricky. Because a Sadist, or more specifically someone with 'Paraphilic Coercive Disorder' could potentially be terrible at one of those relationships, and they're usually the reason for a lot of people being disillusioned with that particular lifestyle. It's a problem, but it also has solutions. Obviously a standard observer into the community would've seen the bare minimum of stuff which has been known to use, including the humble riding crop, which is basically a non-marking torture device. A hideous idea to some, and a titillating idea to others, so the people who know about it try not to judge, and the people who don't, try not to find out.
So what I'm saying here is, Aggressive or Violent sexual tendencies are necessary to have a very large amount of caution with. Obviously someone who does the research and exhibits self-control and finds a fellow interested party could have a fulfilling and non-harmful sex life, but currently it's equally likely to be taken up by someone who has either a) no idea what they're doing or b) far, far more sinister interests. And those people could cause serious damage to society if allowed to do their 'thing'.
So currently society (at least in America) has 'Safe, Sane and Consensual' as a legal parse for this kind of activity. Usually it's a verbal agreement, which is why 'safe words' are so often mentioned in the life, because it spells foreknowledge and contingency, but for more 'formal' soirees, it can sometimes need to be written. And that's to prevent rape charges from being wrongly applied to people.
Essentially it comes down to: It's a fine but extremely well regulated line, and a smart person can still indulge in their fetishes without crossing that line.
3. Pedophilia.
This is the gut-punch of the entire story, because in current society it is mired in fear and loathing, and so is almost impossible to discuss frankly. But I'll attempt to do my best, so if this is a trigger, best you stop reading.
Keep in mind I'm using Pedophilia as a word for the act, not the interest. Not politically correct, but easier.
Essentially because of the stigma and legalities involved in Pedophilia, we're not actually sure of the emotional damage it causes to a child. Naturally kids who have had incidents with it in the past have a higher chance of showing some undesirable traits upon growing up, but again we have no way of knowing if it is because of the stigma, because of the misplaced anger when people find out - the secrecy, or the act itself. Some research (Read: Practically baseless) has come up with the idea that earlier contact with sex can lead to a proclivity towards more extreme tendencies when older, but taken out of a sexual context, if I was snowboarding from the age of 6, I'd be doing some pretty massive tricks at the age of 24.
Add to this the parents. Definitely a terrifying prospect for anyone, to find out that their child has been sexually active, consensually or not. The natural protectiveness of the mother and father comes into play here, as even if there was proven to be zero mental affectation (which seems unlikely) upon a child who had a sexual encounter, the natural reaction of the parents would be an angry backlash - especially in today's society.
So, there's a maybe hanging in the air, but it is terrifically slight, and completely circumstantial.
IF there is anticipated to be a highly sexualized culture in the future (likely), and IF a lot of the stigma is taken off less common relationships (varying degrees of likelyhood), IF someone is willing to completely destroy their reputation and be incarcerated in order to attempt to prove that a child engaged in sexual activity with no shaming, secrecy or backlash will be perfectly mentally healthy (Very unlikely) and IF that research comes up correct (not even going to guess), and then IF children are well-educated about what the hell is going on in society then MAYBE there will be an extremely small subsect of parents in the future who are happy to have their children be sexually active with older people, and the stigma of society and backlash on the pedophiles will probably damage the psyche of the children anyway, and depending on age and gender it can still cause some extreme physical damage anyway.
So in an attempt to be as neutral and frank as possible, I don't see it being very likely that pedophilia will be acceptable anytime in the foreseeable future.
To follow the tangential lines which wierd has put down: Homosexuality and Pedophilia currently both are certain to cause mental trauma due to stigma and backlash, Homosexuality and Pedophilia both May cause physical damage to the participants if a certain amount of care is not taken, but Pedophilia, and not homosexuality, currently has some evidence to show that 'normal' sexual contact can still cause mental scarring. Add in that a homosexual above the consensual age is well aware of their choices, their activities, and the expectations, and that a child is generally 'blissfully ignorant' of the whole situation, hence there even being a consensual age, and it actually comes close to being empirically provable that sexual contact with children is morally wrong.
The only real allowances I can give on the situation is that it is likely that in a highly sexualized and well educated society it is likely that the legal age of consent will have reason to be dropped a few years. But certainly not many, and that still heavily lies upon tradition and stigma.