Nannyogg, with respect, the op doesn't have to present an argument. The default is not having a baby. The person who wants a baby has to make the case.
I hope I don't cause offence but I'm going to be really honest here. I had DS because I was getting on a bit, didn't want to miss out, and everybody told me how fab it would be.
He's here now and he is the light of our lives, but I realise now that my reasons for having him were a bit rubbish. I haven't found it fab, unfortunately. I'm getting there but it has been the hardest time of my life by a million miles.
All my ante natal lot are on their second now, and I'm thrilled for them as its what they want. But I already drifted in to one major life decision, and I'm not doing that again. DS is loved, adored and wanted. But one is enough for us.
Also, and again with greatest respect, it is simply scientifically impossible that two children are easier than one. Of course, they entertain each other (although my mum spent our childhood mostly refereeing and pulling us apart) and that brings its own joy. But much of the work will be doubled. Shopping, cooking, laundry, cleaning, entertaining, organising, etc etc.
Your already hectic workload will double, as will many of your costs. That is mathematical fact.
Also, it is pointless to ask parents of more than one if its a good idea. Their kids are here, loved and adored like all kids are. So they aren't going to be objective. I love and adore my DS but that's not the same as thinking that having him was the right thing to do.