I don't think people are offended by the idea of spending a couple ours with their friends drinking tea and eating cake Momma
I think they just dislike the increasing commercialization of a new life and the whole pantomime that surrounds it.
It used to be get PG, tell people, have a scan to make sure all is well and you may or may not find out the sex, have the baby, name the baby, tell people the name and sex, people buy the baby a gift and send a card.
There may or may not be a Christening and a first birthday party.
Now it's:
Get PG
tell your parents via a 'you are going to be a grandparent' card, or a video to be posted on YouTube.
Get 'congrats on being PG' cards
Get a 'gender scan' as thought that is the primary reason for it rather than an optional bit of info,
Have a gender reveal party with various bits of party tat, balloons and a cake
Tell everyone the baby's name eleventy billion weeks before it's even born,
Have a babymoon
(we used to call it going on holiday while we were pregnant)
Get greetings cards specifically designed for to and from the unborn child, AKA the bump
Get a late private 4D scan so everyone s intimately acquainted with this child's face via posts on Facebook and instagram before it's even born
Have a baby shower with assorted party tat, balloons and a cake
Have the baby (massive anti climax by now because everyone's had said baby rammed down their throats for months already)
Have a naming ceremony if not bothered about a Christening. What's the point? We've known the name since you found out the sex at the scan. 
Have a first birthday party with assorted party tat, balloons and a cake.
Emily photographer to 'make memories' with a Cake Smash (ironically probably the one and only time this child will be allowed to taste sugar for the next 10 years)
Then the child gets a 'prom' and a trip in a stretch limo when it leaves primary school, then again when it leaves secondary school plus a Sweet Sixteen party on top of the traditional 18th and/or 21st.....
The child gets engaged except this involves going to some fancy romantic destination in order to be officially proposed to, completely unspontaneously, where the proposer gets down on one knee at a time and place agreed by the bride in advance and produces the ring that has already been chosen by the recipient in order that this ridiculous non-surprise of a proposal meets all the desired criteria.
Put non-surprise proposal on instagram.
Then this baby gets married and goes on a four day Hen or Stag party.....
Then the wedding where it's now almost obligatory for some members of the wedding party to break out into some sort of rehearsed and choreographed hilarious song or dance routine which is supposed to be a surprise but is now so ubiquitous that people are totally prepared for it.
Post the video on YouTube
And then, most revoltingly of all, pay a photographer to do a 'Trash the dress' shoot, where your beloved groom does a well rehearsed push of his darling bride into a muddy puddle in her wedding dress.
This is why I don't like Baby Showers. It's nothing to do with disliking drinking tea and eating cake.