I don't really get it either. I honestly think there's a number of motivations.
First, some people just don't want to see ads at all. I'm sympathetic to this. I use ad blockers. I don't feel bad about that. But it's not really a reason to oppose contextual advertising.
Second, a lot of people don't really understand what targeted advertising is. I think some people think Meta or Google are selling a zip file saying "Bob Smith of 1234 Main Street like Lego, trains and polyamory" when an advertiser doesn't actually care about you, personally. They care about an audience. This is a group of people with some defined set of characteristics like "Men aged 18-35 that live in the Pacific Northwest and like fishing and hiking". And they're not selling that data. They're selling access to people who match a profile.
It's a little trickier with third-party data services and cookie matching but all that really comes down to is the platform creates an ID for you and passes that to the advertiser so when they see you, they can build their own contextual data. That may sound nefarious but the ID is just a random string. It's different for every advertiser so you can't match across advertisers. Users can pretty much reset that ID at any time and all that matching data is effectively orphaned and lost.
Now we can, should and have had conversations about what targeting is allowed. Generally, location can't be too specific (eg typically only down to a city or town). There have been issues too with illegal discrimination (eg [1][2]).
I also think we should generally ban all advertising to anyone under 18, targeted or not.
So personally I see advertiser targeting capabilities not behavioural contextualization of preferences to be the issue to tackel.
[1]: https://www.washingtonpost.com/technology/2022/06/21/faceboo...
[2]: https://www.theguardian.com/technology/2011/aug/24/google-se...