That's not a very good analogy. People who are on bail awaiting trial have been charged with an offence, so the CPS at least are convinced there is a case against them, and that they are likely to be convicted. Your initial reference was to people who are on a watch list. Now some may be on that list because they are convicted terrorists, but other will be there because they are simply suspected of involvement in some kind of offending, or are known to sympathise with the ideals of, say ISIS. If we go down the road where people's rights can be restricted in the basis of mere suspicion, that is a very slippery slope. The police for example can arrest you on suspicion of having committed an offence, but have to then quickly establish their case sufficiently for you to be charged, or let you go.