It's up to all of us to make sure they don't win, if that means taking the knee stays in football for the conceivable future than so be it. Until it gets through to people the point needs to go on being made. As far as the Euro's are concerned they need to start identifying people who choose to boo and then they can be dumped outside if they are not prepared to show the respect they should.
But this is the problem. How do we 'win' in this? Taking a knee hasn't stopped racism and was never going to - it's actually proven counterproductive by showing trolls how useful it is in getting under players' skins. So now the only way to 'win' is to keep making a gesture with no external relation to racism in football, that you weren't making a year ago, when it clearly isn't working?
And the second point, about booing, just exemplifies how progressives just never learn. How many times do people need to be Streisand Effected before they get it? If stewards began trying to throw people out for booing during the knee, one of two things would happen:
1) Those fans decide to boo at kick off instead, or at a point during the game, which makes their point exactly the same way. At that point the only option is to throw out anyone who boos at a football match - something that makes anti-racists look authoritarian and plays into right-wingers' hands;
2) Those fans decide to do it anyway and the stewards are faced with the option of risking their safety by trying to throw out dozens of probably drunken fans at once, or calling in large numbers of security guards and having it likely spill over into physical violence which, once again, exacerbates the problem.
As far as I can see the only realistic option is to come up with concrete achieveable demands which don't affect the powerless in other areas (eg. removing online anonymity), such as mandatory lifetime stadium bans for racial abuse, and to have some kind of solid threat behind it like a general players' strike. Even then, you'd be inviting clubs to monitor their fans far more closely and giving them an excuse to crack down on 'troublemakers' of all kinds in the name of pre-emptive action. But you'll never be able to eliminate racism completely, any more than you would any other bad thought. You just find more effective ways of combatting it.