i went up to the RC altar with arms crossed (in order not to receive) and then had to work out how to say 'i don't wish to take Holy Communion' without opening my mouth! (the Holy bread was coming towards my mouth very quickly!)Ummm, what about remaining seated?
in many catholic and protestant churches, people worship God sincerely. if this is the case in any church i am visiting, and especially if they are following tradition (or trying to return to it), for example by believing in Holy Communion as a sacrament, not just a symbol, then i like to worship together with them as much as is appropriate (depending on the theology there).
i have occasionally visited churches where i feel very uncomfortable, due to various theological errors or lack of love for God; then i sit politely and do not take part.
the catholic tradition of people going up to seek a blessing at the time of Holy Communion is a beautiful and humble tradition and i think it is good to follow it when visiting the church.
in the example i gave; i found a catholic church near where i was staying when i had to be in ireland to take an exam.
the day before my exam, i went to the catholic church and there was a beautiful liturgy and the priest talked to us about trusting in God and seeking His will.
it was a weekday, and there was no orthodox service anywhere near that area, so i went to the catholic church.
i was greatly encouraged and went on to pass the exam.