There are probably downsides and ways this will screw up real relationships but it will certainly increase the cost of spam.
- Every contractor (plumber etc) you hire will ask you to please add them to your contact list first so that they can message you.
- After a while of half their clients not doing that and lots of fees on their end, contractors stop providing a phone number at all, asking you to please install ContractorApp to communicate with them.
I disagree about the we-adda-baby-itsa-boy issue. I don't see how that'd apply given that you can charge them $1 from the very first message.