Interesting comments. Ceri does make a vital point about acting in general, which I think is evidently true - the more personal 'blocks' one can overcome in one's search to craft another character, the more original and striking each separate creation will become. And this is, simply put, what makes for 'great acting'. In an ideal world, no experience should truly be considered off limits to the actor. I was reading only the other day about one of my personal heroes, Daniel Day - Lewis, whose commitment to role creation is such that he has been prepared to do such things as train as a boxer for 3 years, lock himself away in solitary confinement for several months, learn how to skin deer by hand, build a house using only 17th century tools, etc. - all activities which I am sure pushed him far 'out of himself', and allowed him to discover new potentialities he never knew he had. This sort of journey of self - discovery and pushing the envelope should be the ambition of us all as actors.
BUT...(and this is a significant but...)
Two of the most important issues that I think have been raised on this thread (never, perhaps, addressed) are these:
i) There is a huge qualitative difference between how we define levels of 'intimacy', and one of the original questions (very pertinent) was how far is the individual actor concerned prepared to go?. It seems to me that there is a whole range of what might be termed 'intimate' scenes that the actor might have to involve his/herself in, namely: simulated kissing/foreplay; individual nakedness; nakedness alongside a group of fellow actors naked; simulated sexual intercourse wearing clothing; simulated sexual intercourse in the nude; full-on penetrative sex(!) etc. These elements are not, necessarily, interchangeable - a nude scene in which the nudity is played for comedic effect, for instance, may be less problematic than a scene simulating sex which is fully clothed. There are scenes which lack all true 'intimacy' but which are nevertheless explicit, such as rape scenes, which many actors may find more difficult to cope with than more 'standard' sex scenes. Some people would be happy to simulate masturbation on film, but reluctant to strip to the waist for a scene and so on. Distinctions *do* need to be made - because being happy to be naked is not the same achievement as being happy to be seen being sexually explicit- and the only thing in this regard that can be taken from Ceri's comment is the notion that, in an ideal situation, *all* such 'blocks' whatever will need to be conquered in order that the 'whole actor' can emerge.
ii) Female and Male reactions to this issue may be very different. I think this is a vitally important point (and, in a way, I'm hardly qualified to talke about the female perspective, but still...)...what I note is that, by and large, women are far, far more 'reluctant' to be involved in scenes of a sexually explicit nature than men (at least, they question it more). I find it a little dismaying that the last couple of posts seem to have been forced into fighting a bit of a reargaurd action against the assumption that 'if you cannot overcome your blocks, you'll be no good as an actor', when, in fact, this seems far easier to say from a male perspective in relation to sex scenes than it does from a female.
All that appears clear to me is that, in the very act of sex (simulated or otherwise), the man 'offers', and the woman, invariably, has to 'receive'. This gives any male in a sex scene the benefit of being in 'control' of the scene; it means they do not have to (in any sense) 'open' themselves to the other partner. It may be that this makes it infinitely easier for male actors to 'switch off' or 'go somewhere else' when they are acting having sex. For female actors, there is a presupposition that, even when simulating, they are going to have to remain 'open' to their partner; to allow themselves (unless the scene is very deliberately skewed) to be dominated by their fellow actor; and (9 times out of 10) to lose control whilst their partner is (tacitly) allowed to retain it. Thus, women in sex scenes are placed into a far less enticing, far scarier and more vulnerable position than their male acting partners tend to be. If this generates more corresponding anxiety in women when the matter of performing a sex scene rears its head, whilst men continue to hand out platitudes about how easy it is to cope, then it doesn't seem to me to be anything to be surprised at, or, indeed, ashamed of.