People who do illegal things are:
il·le·gal
(ĭ-lē′gəl)
adj.1. Prohibited by law.
2. Prohibited by official rules: an illegal pass in football.
3. Unacceptable to or not performable by a computer: an illegal operation.
[I][B][B][B][I]n. [I]OffensiveA person who is not legally authorized to live and work in a country.
Therefore, I conclude calling someone an illegal is neither inhuman,
discourteouse, or inaccurate so long as they meet a reasonable standard of proof that what they have done or attempted to do is in fact an illegal act. If it makes you feel better, you can call them "CRIMINALS".