Roman,
Thanks for your question. I had to think a while before contemplating a response to your question, which is a very valid one, I must say.
You are right, that any one can basically do whatever he/she wishes. E.g. if you are living in USA, for e.g., and you want to watch a porno movie, you can do that, regardless of whether you are a muslim, hindu, christian or jew. Right? So there is a freedom to do as you wish. Similarly a muslim can wish a non-muslim and treat it as just a friendly gesture, “harmless” as you put it, and be happy.
Islam is significantly different from any other beliefs due to one striking factor. Other beliefs including christianity, budhism, jewish beliefs, hindusim reflect a methodology to reach out to God (by whatever name) and, in cases of divine religions, to stay on the path of righteousness as prescribed by the Prophets of God.
On a purely fundamental level, Islam is not a religion but a ‘deen’, meaning ‘Islam is a way of life’. (Many people even muslims might be amused by this statement, but it is quite true.) So the right way in Islam encompasses our whole lives and not just the rituals of prayers. Every single thing a muslim does must be according to Islamic teachings. That is not to say that Islam mentions every single act we do, rather it provides guidelines on what is permissible and what is prohibited. In between there are many other states (these include recommended [mustahib], disliked [macroh] etc).
If a new situation comes up, a muslim can adopt one of the two ways. Based on his/her knowledge, determine what is permissible and what is prohibited and follow that. If he/she feels that their knowledge of Islam is poor or if a scholar is conveniently available, to get the opinion of the islamic scholar on the permissibility/prohibition.
Once this stage is over, a muslim knows what he/she can do or cannot do or should/should not do. Then it is their intelligence whether they do it or not. No one can stop them.
The basic concept is, ofcourse, that there is a hereafter, where we shall be answerable to all our deeds which we did in this world. All of us do some good deeds and some bad deeds. So if we did more good, then we will have a place in heaven and otherwise it is hell-fire.
So based on the above “brief” summation, I hope it is clear that while a muslim can do pretty much as they please still there may be an opinion by muslim scholars on the permissibility or prohibition of any act.
So while there is an opinion by muslims scholars that wishing a non-muslim for their religious ceremony is prohibited, a muslim can chose to ignore it and carry on with however they wish. We always hope, for the sake of that person, that the good deeds by that muslim will ultimately out-weigh these transgressions for a successful hereafter. Also, Allah, in His infinite mercy, can forgive all our sins, or whatever He choses to do.
Adios!
(Due to my limited knowledge of hinduism/christianity etc, if you feel that any statement attributed above to these faiths is incorrect, I hope you won’t be offended)
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