As to why people honor Sunday, you probably know the Scriptures:
Acts 20:7 (NIV) On the first day of the week we came together to break bread.So the early church clearly met on the first day. But we can assume they met nearly every day (see Acts 17:11, for example) and there is no reason to suggest that the principle day of worship, the "Lord's Day", ever changed from the Sabbath. This is when Scripture tells us that Paul would preach in the Synagogues, or elsewhere if they would not have him.
1Co 16:2 (NIV) On the first day of every week, each one of you should set aside a sum of money in keeping with his income...
Of course, this is a issue that people can have deep "religious" (in the worst sense) feelings about and can quickly become divisive and pointless. And Scripture could not be clearer on this particular controversy:
Col 2:16-17 (NIV) Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day. These are a shadow of the things that were to come; the reality, however, is found in Christ.Those who insist that Sunday is the new Lord's day point out that the Sabbath was fulfilled in Messiah. Indeed it was, and this is highlighted and specifically singled out in Scripture. (See Hebrews 3-4) But this does not mean it is forbidden that we should honor the seventh day, if the Lord so leads us. After all, it made the big ten; and there is no other of the ten commandments that anyone feels like we should not adhere to in the New Covenant.
As well, Sunday should be celebrated for the new life that comes from the rest we "enter into" in Christ on Saturday.
Our position and understanding of the Saturday/Sunday issue is that there is room for freedom.
"The Sabbath is for man, not man for the Sabbath". And Laura and I enjoy celebrating it as the Lord leads. For this reason we love to meet on Erev Shabbot, or Friday night. "And the evening and the morning were the first day." By God's reckoning, and Biblical reckoning as well, the day starts at nightfall. So, we are sort of "stealth" Sabbath keepers. This does not trip up the legalists who think it a sin to worship on the Sabbath, nor encourage the legalists who think themselves better if they do. Even the latter are often ignorant of God's reckoning of days.
In Dallas we had a Friday night bible study in our house, went to a Messianic gathering on Saturday morning, often to another group on Sat night--or an "early church service", and then to church on Sunday as well. Why not meet on every day we can? This is our bounty and freedom in Messiah. 10,000 teachers, and the richness of fellowship should not be missed.
As to making a big deal about this, Scripture could not be more clear:
Rom 14:4-10 (NIV) Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand. One man considers one day more sacred than another; another man considers every day alike. Each one should be fully convinced in his own mind. He who regards one day as special, does so to the Lord... and gives thanks to God.. You, then, why do you judge your brother? Or why do you look down on your brother?..So we have the direct command of Scripture NOT to judge men by days they choose to worship. We must remember as well that "each one should be fully convinced" and "not judge in this".
All days are ours, and we should embrace the true rest, and not be diving to hug shadows.
To have a basic instinct to be divisive about this, then, is a clear sign of being out of step with the Holy Spirit. The Lord looks on the heart, and is looking for hearts that care more about people than days, and more about God than people.