I realise there are similar questions around this topic, however, I think this is sufficiently different/focused not to be a duplicate. I hope it doesn't sound like a soapbox piece.
HTTP/2 effectively mandates TLS, since there isn't a mainstream browser implementation supporting h2c.
Whilst the aims of the "SSL everywhere" movement seems reasonable, I'm unconvinced. I'm concerned that in practice, it will make the web less secure whilst creating the illusion of security.
In many parts of the western world, bandwidth exists in sufficient quantities for local caching to be overlooked as a concern, it certainly isn't universal - indeed, reliable connectivity is an issue in some locations, and a caching proxy is an appealing solution.
TLS proxies already exist that can be used to mitigate this, provided someone is willing to install a root CA to accept re-signed content. Some corporate desktops do this as part of a standard build. Forcing TLS on web users will encourage this practice.
There will also be cases where in lieu of installing a root CA, users will become accustomed to accepting self-signed or suspicious certificates, potentially to a level where it becomes automatic even for sites that really shouldn't have this issue.
There's a psychological impact to churning out the message that "this site is secure" - it predisposes users to think that if they can see a secure padlock/green tick/whatever then they don't need to concern themselves with what information they're sharing, and why - legitimate sites can be hacked, less reputable ones can get SSL certificates, and if there isn't at least one intelligence agency or organised crime cartel that has a copy of a real root CA cert, then I'm a teapot.
I'm hoping you can convince me I'm wrong; are there strong technical reasons for browsers mandating TLS for http2?
Afterthought Whilst I fully appreciate the concerns raised by the NSA and GCHQ getting caught spying on popular web-based email and social media platforms, it bemuses me that platforms run by multinational corporations are seen as more trustworthy - some, if not all, of them, are gathering intelligence - rebranded and justified by targetted advertising.