Ever been in a situation when you thought you were having a friendly chat, and then it turned out someone was trying to sell you something? Not a company you’d want to do business with.

Facebook has just announced that it is testing an advertising model in which companies can buy ads that appear in your Newsfeed – whether or not you’ve shown any interest in those companies.

This isn’t surprising, but it does feel like one of those tactical decisions that might make more money for a while, but is a strategic disaster.

The issue isn’t that ads will appear in your feed. We’re all used to having advertising turn up in all sorts of places we’d rather it didn’t. The line being crossed is that Facebook is actively trying to blur the line between a conversation with friends, an endorsement (it’s Like button), and an outright ad.

This has already happened on mobile, where ads are already more or less indistinguishable from a friends post:

It’s working very well for Facebook and for advertisers who know what they’re doing. Now Facebook is looking at bringing it to the desktop.

Facebook is selling advertising – we are the product. The problem is that as it focuses on the advertisers, it risks undermining the service 800m people are turning up for – a good way to communicate.

Imagine your mobile company decided which messages got through to you. Imagine it promoted those calls from people who used their services more, not necessarily those you were closest to.

That is Facebook’s Newsfeed. That’s why we all get a lot of information on Facebook from people we know, but are not our best friends.

Now imagine some of those messages started being friends recommending products to you – because your mobile company promoted conversations that mentioned products. That’s Facebook Likes appearing in your Newsfeed.

Now imagine that companies can pay to have relevant friend recommendation messages get through to you. That’s Facebook’s Sponsored Story advertising product.

Now imagine any company can pay to get a voicemail through to you, and it’s not totally clear whether the message came from a friend or not. That’s Facebook’s Newsfeed Advertising product – the example shown above.

At some point you’d stop using that mobile company to communicate. The core purpose of such a service is to allow you to communicate and share your life with who you want to ensure messages are passed along accurately, and for the service to act as a gatekeeper for people that know you.

If the gatekeeper starts letting people through because they pay them, and aren’t transparent when they do so, you’ll find a new service.

Dangerous strategy.

Alexis Dormandy is the founder of LoveThis. He’s  @adormandy on Twitter.