I block ads and I still buy things. The world won't collapse if advertising is curtailed.

Consumer habits will just become more unpredictable- and small companies could compete with big companies that spend billions on marketing.

I don't agree. The more likely outcome would be complete domination of big brands because they own the mindshare (e.g. people will remember Amazon.co.uk, they will not remember hundreds of small businesses too).

Even if you were not directly influenced by advertising, you probably were indirectly through word of mouth.