> 99% of the opposition to Signal integrating cryptocurrency payment seems to be from people who generally disagree with the idea of cryptocurrencies
Most crypto projects are a scam, but some are great. I do hold bitcoin since I started doing research on cryptocurrencies for my bachelor thesis on that topic back in 2013.
Adding cryptocurrency capabilities to Signal is a very bad idea for many reasons.
It has almost no practical value for users of Signal. Those who want to use a wallet for the currency of their choice can always download one and probably already did so. That's the superior solution because it's not just coin-agnostic, but promotes choice: if it's not a good wallet they can change the app without suffering though network effects, something they can't do with their messenger.
The regulatory environment for messaging is drastically different from the regulatory environment for cryptocurrencies. The latter is less consistent, less clear and still faces high regulatory risks in some markets. The first one has clear advocates and strong theoretical backing in all democracies while the second is still on very shaky grounds with varying degrees of good will in society. I have yet to read an argument why stretching one product to fit both environments might be a great idea, or even just a prudent choice of risk management.
It is hurting Signals reputation, which is Signals main selling point. For several reasons:
That direction surprised many people as Signal is far from a feature complete messenger. Almost everyone agrees that there is real work to do regarding, for example, multi-device support, history portability or the decoupling of phone number and identity. A wallet for an almost unheard cryptocurrency might feel random to many, given the many features users are still waiting for.
Another reason for why this feature is hurting Signals reputation is that cryptocurrencies, just as you said in your comment, are controversial for many. Some projects are more, others are less controversial and MobileCoin - for now - seems to be in the more suspicious camp.
It's generally, in branding, not a winning strategy to tie your good brands to your bad brands. You would want to keep them neatly separated until they are both successful just so that you can drop your less successful brands without putting your winners at risk. ... and you would do that despite believing in the success of all your projects.