I personally thinking profiling has a benefit... but I understand it is a hot issue. To use one of the examples above:
Check all young islamic/foreign males that are carrying a bag onto a bus that may be used to conceal an explosive device
When you look at it like that, I can see how some people would find it repulsive and ignorant. But lets look at how it would work in practise. On 7/7 young muslim men got onto buses and tubes in London, at a time that we were all aware that any such threat would most likely come from young muslim men. If each of them were checked, the 7/7 attacks could likely have been prevented. As there were 4 seperate attacks, the likelihood is that such a rule would have at least lessened the overall devastation. If they knew they would be checked, it could well have been pre-empted. Because there was no such checks, people died.
So you could then say:
Extensively check all passengers who are boarding the bus with a bag
This would be a more fairer way of doing it, but is there much point? Because 6 year old girls and 60 year old grandfathers are not likely to blow up a bus. I'm not saying every muslim is, but the demographic for blowing up buses at that time was pretty much them. The time and cost and inconvenience that it costs to extensively search anyone is pretty much wasted. We can round it out to an age group and any ethnicity to be more politically correct, but I don't see the point because we know who the likely suspects are so why inconvenience more people than necessary? If young white men started to blow up the buses, we could then check them as well, so I wouldn't see it as racism, or prejudice. It's simply identifying likely threats and taking extra steps with them.
Is one particular muslim male more likely to blow up a bus than I am? No. I may have a troubled life and he may be a quiet devout. It's entirely forgivable for the police not to forsee the actions of a single nutjob. But in my view, it's not really forgivable to lose lives because they didn't recognise trends and act on them accordingly.
I see profiling, and police profiling especially as efficient. If it had saved lives in 7/7 I wish we had used it. As for how unfair it would be? If females in their mid twenties were more likely to be bombing buses, I would happily be checked, for I have done nothing wrong and I would understand that it's other people of my age group that have let me down in this respect. It may even be enough of an inconvenience for me to actively rally to change the opinions and ways of my demographic, something that didn't appear to really be happening enough in the islamic community back at that time. They condemned it, but had it hit their own rights and convenience, they likely would have made a more concertive effort to stop it.