It is clear from reviews of his recent work, and spats on Twitter and in print, that some people now seriously dislike Ricky Gervais. Their hostility will be revived by the arrival last night of a six-part series of Derek, his comedy about a vulnerable, middle-aged man working in a care home for the elderly, which was controversially launched on Channel 4 as a one-off last year.

Early adverse reaction has described the sitcom as "mawkish and misjudged", while the longer run is likely to revive the view that the show is an exercise in bigoted cruelty. Some critics have suggested that as his career has progressed, Gervais has deliberately escalated the level of offence: from PC-baiting material about disability and race in The Office and Extras, to a direct dramatisation of disability and bigotry in Life's Too Short – based on lead actor Warwick Davis's own experience of dwarfism – and then to what some observers have interpreted as the ultimate exercise in discomforting viewers: mocking a figure with a disability in Derek.

However, the character of Derek Noakes predates Gervais's TV fame. He featured in his 2001 Edinburgh standup act, the summer that The Office was first shown on BBC2. At that stage, Derek was explicitly a victim of sexual abuse – there was a sequence in which he gruesomely described an encounter with a relative. If anything, he has been toned down for the Channel 4 show.

The question of what Derek's problems are is central to the controversy. Objectors to the pilot took it as a given that the character is disabled and that therefore the show mocked someone with a disability. "Autism" and "learning difficulties" have been confidently cited.

This certainty surprised me, because no such diagnosis was revealed in the script. So – chairing a Q&A session with Gervais – I raised this with him.

Gervais insisted that the character is not intended to represent a specific disability; he is simply naive and gullible. So what about the body language Gervais adopts, in which Derek's torso lurches forward, like someone auditioning to play Richard III, and his mouth consistently lolls open? Again, Gervais argued that the character is merely maladroit, with a dodgy hairstyle. With the kind of challenge familiar to those who have engaged with him on Twitter, he asked what is medically wrong with Frank Spencer, a previous naïf played by Michael Crawford in the 70s sitcom Some Mothers Do 'Ave 'Em?

Well, Spencer was, in a vernacular acceptable at the time, "a bit slow", but the greater scrutiny of Derek reflects the increased sensitivity in this era.

The many implacable enemies of Gervais will suspect that he denies Derek is disabled because that removes his opponents' weapons. Personally, I accept that Gervais is not portraying someone living with an identifiable syndrome. But, for me, this is a weakness of the series.

Actors are generally happier playing specific characteristics: an ex-footballer whose career was ended by a broken leg, rather than just a bloke with an unexplained limp. And the vagueness sometimes destabilises the show.

There is an obvious gap between the visible intelligence of Gervais and the inarticulacy of the character. Derek says "wroted" instead of "wrote", but is also capable of referring with some delicacy to a stream on a beach "coming back on itself". This sense of a hole in the role, through which the creator can be seen, is exacerbated by the fact that Gervais – or, at least, his showbiz persona – is so familiar.

Performers such as Alec Guinness and Paul Scofield used to argue that actors should be wary of giving interviews because the profession demands the ability to disappear within a part. But contemporary actor-comedians such as Gervais, not only chat-show regulars but also constantly visible on social media, are as far from that mysterious ideal as it is possible to be. The risk is that a proportion of viewers will always be judging the public personality – and, in Gervais's case, controversy – as much as the work. It's intriguing to speculate about how Derek would be received if played by an unknown actor.

I find it hard, though, to agree with those who say that the show is cruel. Whereas Frank Spencer was the butt of the joke, Derek is always ultimately the hero: someone whose kindness and thoughtfulness may be mocked, by characters who are clearly set up as villains but whose friends at the care home reward him with warmth and understanding.

In fact, I have always thought that the trait Gervais needs to watch is not callousness but soppiness; in all his TV projects since The Office, there has been a strain of romance or redemption. The drawback of Derek is not that it is cruel about disability but that it is often soft on a character whose identity remains too vague.