I have recently come into contact with a party unnamed who has a nasty little habit. Scattered liberally through their communiqués I find this grammatical construction:
Do please drop into my office this week.
This event is going to be really useful – so do go along!
Originally I, sunny soul that I am, assumed that this meant I had a choice- perhaps I would ‘drop in’, perhaps I wouldn’t. I might go to the talk, but then again I might just watch Buffy the Vampire Slayer instead. This led, inevitably, to problems. The next step was to challenge the orders- ‘I won’t be coming to your office because I am not available that day.’ Of course, the person in question responded with a cheeky little ‘That’s completely up to you.’ Well, it wasn’t, because as you can probably imagine, they had all the power in our relationship. And I let it go so far that eventually I was penalised for choosing not to do what I had been told. And then it hit me.
The attempted tempering of the imperative with the use of the auxiliary verb 'do' is fundamentally passive-aggressive in nature.
In life, if you want someone to do something, firstly you choose between an ORDER and a piece of ADVICE. The imperative - ‘Come here!’ ‘Go along to the event!’ - can only ever be an ORDER, even if you add an auxiliary verb with the basic intention of shifting the spoken emphasis of the sentence onto the auxiliary verb - ‘DO jump off a cliff’- rather than the main verb - ‘JUMP off a cliff!’. (Say these two sentences out loud and you will probably hear a difference.) So the listener will know that they are being ordered to jump off a cliff either way, but might be fooled into thinking it's 'polite' because of the unusual word-stress patterns. This is particularly annoying in written texts, where the word-stress patterns are only in the mind of the reader anyway.
If you choose not to use an imperative because it's too forceful, the English language gives us a first beautiful choice of the more elementary modals: 'You can', 'You should' and 'You must/ have to'. All of these can be used with varying degrees of coercion, yet retain a basic honesty. Either you can or you can't; either you should or you shouldn't. And that leaves the listener with the same basic choice they always have in society- to believe the person who is telling them what to do or to take the risks of disobedience. We're all used to that choice (since early childhood) as it's part of the way we understand personal freedom under the restrictions of modern society.
Alternatively, you can bloody well ASK- 'I would like you to', It would be great [for me] if you', 'Would you...?' 'Could you...?' but my example speaker appears incapable of ever taking responsibility for their own desires and admitting that it's them who WANTS rather than the listener who SHOULD.
'Please feel free to' and 'You're welcome to' mean that the speaker feels they have all the power, and are thus MARGINALLY less offensive than 'do', implying as they do that either the speaker does have all the power, or that he/she is slightly more at home with his/her control-freakery/ megalomania and doesn't need to resort to rhythmic conjuring tricks to disguise it.
Finally, what’s wrong with a first conditional- 'If you jump off a cliff, then this will happen? You can include yourself- 'If you jump off a cliff, I will feel warm and fuzzy inside,' or attempt a conjecture about the personal effect it may have on the listener- 'If you jump off a cliff, you will probably achieve more tonight than if you look at facebook,' or even, without any falsehood, about the greater good- 'If you jump off a cliff, the world will be a better place.'
'DO do it' is therefore even more irritating than 'If I were you' (another almost inevitably dishonest manner of framing advice since it tends to be accompanied by the unspoken 'But thank God I'm not').
To put it differently, when you want a dog to do something, you use the imperative- 'Come here', 'sit'. To add 'Do, please,' to this would scramble the poor dumb animal's brain and is therefore cruel. If you want to treat people like dogs, at least be honest about that.