There are both nice England supporters who will wish Wales well and England supporters who, if you tell them they haven't been away from home yet this tournament, will be quick to tell you that Wales wouldn't survive without England or will shout "come on England" in the Millenium Stadium when watching the UK play Olympic football - a country of 68 million having both good and bad to it shocker!!
England football does what they think is right for England football though: they've pushed for an Olympics' team because it's right for England despite concerns about what it means for other home nations independent football status, they broke away from home nations youth cup because it was right for England despite it being a knock to other home nations and they pushed David Gill to be lead representative for governing body despite it being the Welsh official's turn because it was right for England football.
There are also many in Wales who will be quick to enjoy this summer but weren't bothered by 2016 because they don't want to see Wales as a nation in any small way. Welsh Tories are second biggest party in the Senedd and basically ran a campaign of "we're doing too much thinking for ourselves" while several other parties picked up hundreds of votes wanting to unwind any sense of nation status. There are MP's (Shrewsbury MP, Uxbridge and South Ruislip MP) in England who would likely agree.
James Collins has right to support whoever he wants, it's really not any different from him saying he'll support Spain now, but doesn't have right to say he's speaking for everyone. A small adjustment to his wording would likely see a different reaction from most.