Everybody is talking about going mainstream and with Bitcoin we do expect this to be happening soon and there are many advantages when that time can come. But there are also disadvantages and one is the fact that it would be subject to much scrutiny and possible regulations.
What we are seeing right now in China which is spewing out many bad news affecting the whole cryptocurrency market is just an example of what can happen when Bitcoin has already reached the mainstream status.
When Bitcoin is just small no big authorities are noticing it but when it started to spread like a wildfire the government interventions via rules and regulations started trekking in BUT we could not also just remain small as Bitcoin has really to grow if we are looking forward to its fantastic future.
In my opinion bitcoin is a grassroots movement. It is p2p which means that governments can't shut it down completely. It can shut down exchanges, sure. but they can never ever stop the actual bitcoin transactions, unless they shut down the internet which is impossible.
I don't get why you think that going mainstream is bad at all. If enough people support btc then the government wouldn't even dare putting these restrictions in. Plus, we don't really need exchanges for bitcoin to survive especially when it goes mainstream. Everyone will either just accept btc directly, or trade p2p without a third party exchange.
And plus bitcoin has already gotten a lot of attention, i don't think that it's going to get much more from governments. Worst case scenario is that every exchange is shut down but i've addressed that. Not really a concern.