I can see both sides. The last time (many moons ago) I got involved was memorably when we sent the Wrexham Front Link packing - early evening and everyone stone cold sober. I wasn't particularly bothered about getting involved but I was in my late teens and peer pressure meant I'd have been Billy No Mates had I not.
Imho the British police are far better at crowd control, they'll exhit a "presence" but the heavy brigade are normally parked round the nearest corner so as not to be provocative but available should they be required.
There are some hardcore nuts in Portugal (who know how to mingle, stir it up and slip away) but most are drunken chavs who'll scarper at the first sign of trouble or throw missiles from a distance of safety.
You could ban the national side from international football and hope they'll lose interest when denied the opportunity to cause trouble but many come from provincial clubs and can wait long spells for international football. I think the first one to be deported was a Stoke fan with previous... so it makes a mockery of banning orders.
Drink, peer pressure, sheep mentality and a British social problem. The media do a fair bit to stoke up simple-minded xenophobia ('Achtung Surrender!') too.