That assumes that they agree with your interpretation of the facts and your application of logic. Logic can be used to prove whatever you like by inputting the facts you chose - Gigo's law.
If you are accurate in your assesment of the facts and if have properly applied logic and if you explain said argument with evidence regarding your facts and said person continues to do what they do then you are entitled to say that they are immoral _in your opinion_. There's a lot of ifs there which should temper you're attitude of absolute certainty a little.
However all you have really done is called them a name. You haven't advanced your argument at all and you may be overlooking the fact that they have facts that you don't or that they interpret those facts differently.
Ultimately if morals are mostly a matter of personal opinion, as you have admitted, then the only way you will swing people to your point of view is through debate. Do you really think name-calling is going to help?
Note that during this discussion I have made assertions about things that you DO, I have made no asssertions about what you ARE.
This is an important distinction to make when trying to explain your views to people without alienating them right off the bat.