Answer: Fundraising is the organized activity meant to generate funds for (usually) a worthy cause. According to your Email, some church members have rejected allowing such activities on church grounds based upon verses in Mark 11. These verses, which are related to fundraising in that money is changing hands at a place of worship, records Jesus' response to moneychangers at Jerusalem's temple.
What the moneychangers were doing has almost no bearing on the issue of church fundraising. The changing of money was a needed service for the temple. Any currency that would be used at the temple (for example, as an offering) had to be exchanged for special coinage. Moneychangers made their money by charging a fee they set for exchanging currency. This business could be very lucrative, in part, because it was so easy to cheat people.
What did Jesus condemn?
What Jesus condemned through his actions in Mark 11:15 - 17 is not related to raising funds as some in your church congregation believe. He was not angry with those in the temple area because money was changing hands. He was mad because they were taking advantage of people! The moneychangers were cheating and robbing people. This is why he said these businesses had turned the temple into a den of thieves (or robbers) in verse 17.
Jesus condemned those at the temple because they were robbing or stealing from others for their own benefit. Raising funds on church owned property by selling goods or food (usually donated) at a reasonable fee and using the proceeds for others who have legitimate needs is a far cry from robbery for godless gain.
It should also be noted that when Scripture uses the word "church" (ekklesia, Strong's Concordance #G1577) it is referring to a group of converted people. It is not referring to a building or other structure owned and used by believers for worship or for an activity like fundraising.
Does it defile?
The church, meaning the members of Christ's body wherever they live and meet, are indeed holy (Colossians 3:12, etc.). A building or plot of land used by them, of itself, is not. This means such an activity like fundraising, on church property, does not somehow "defile" holy ground. This is in contrast to Jerusalem's temple, which was not only dedicated to God but was set apart for special use directly by him.
It is commendable that elderly people, on limited retirement income, still want to do their share in serving the Ekklesia or church. Fundraising activities such as hosting a paid meal open to the public, or selling soda, chips, cakes, cookies, snacks and so on are an excellent way for them to be able to serve and do their part in contributing to the benefit of other believers in the group. The God of the Bible does not condemn activities like these.