There's never any excuse for blatant rudeness, but sometimes it's understandable. Though I've never said anything like this myself, I have often felt like it.
Sometimes to me it feels like the whole school system (and early years) is completely organised around the archaic expectation that there will be parent (usually the mother) available during school hours, either because she's a SAHM or she has a second earner type job that obviously isn't too important.
Parent's evenings (which are actually parent's afternoons), harvest festival, nativity play and numerous other similar events, fundraising coffee mornings, etc, quite often with less than a week's notice and a line at the bottom saying "you are welcome to take your child home after this event rather than wait for the 3pm finish". Great. Cue frantic calling to CM because I don't want my child to be the only child left in the room while everyone else goes home. As someone who is a single parents and relies completely on professional childcare to cope with a job where I am the only person in the company who can do what I do and therefore have to plan schedules accordingly, it would help enormously to have some notice of these sorts of things. I can usually take time off when I need to but it's notice that's the problem. Given that they probably do the same things year in year out why can't they just give parents a timetable of all these things at the beginning of the academic year?
And then the constant demands for money. I now give very little to anything because I am never sure how many more demands I am going to get and I have a budget that I can't go over. I could possibly give more but I have to keep some back for the 100 other requests I might get. TBH I'd rather they just stop it all and I'll agree to set up a DD. They'd undoubtedly get more money because these rather sad attempts at a reason for the money (e.g. your DC's self-designed Christmas cards or 'your child's poem in a published book' 
), in which the school get a 'cut' of the charge, is bound to be less (e.g. £1.00 per pack) than what a parent would give if just asked to donate an amount they could afford for no reason other than bolstering school funds.
I sound angry about all this, but I'm not really. I completely understand that the school are going on the basis of don't ask, don't get, and that if they constantly ask parents for help/money, some parents will say yes some of the time and then the school gets something. They're not expecting all parents to help all the time and I'm aware that putting that slant on it says more about me being defensive than it does about the school being pushy. After all, all this help is for the benefit of our children ultimately and I'd rather the school pursue every avenue it can (especially with the cutbacks in the education budget).
Maybe you caught some parents on a bad day. I bet most are actually quite appreciative of what you do, like I would be, despite my grumblings above. 