Realistically, Man Utd wasn't floated on the stock market for the good of the fans. It was to make money and unfortunately, like NM correctly says, one of the risks of becoming a PLC, is that at any given time, someone can come along and buy you. Maybe the fans should be angry at the men that floated the club in the first place, and basically just whored the club out for merchandising and profiteering, something that just happened to be nicely supported by some success and good football for 8 or 9 years.
Glazer obviously sees Man Utd as a profit making business. Yes he's brought the club into debt by buying it, but he wouldn't have done so if he didn't see it a solid investment. Why would he let the team go stagnant by placing no money in to the transfer funds. I'm sorry, but if you can get loaned over 250 million, you can find 20 million a season for transfers. The club will drop off the pace and lose support if he doesn't allow the manager to spend money, it would be bad for business and therefore bad for Glazer, not to invest in the future of Manchester United.
Tampa Bay Buccaneers won the superbowl two years after Glazer took them over. He obviously is a good businessman, and Manchester United fans, fans of a team on their way down in terms of the success they enjoyed in the nineties (don't expect one utd fan to admit that however) should give him a chance. Quite frankly the pitiful demonstrations buy the few thousand fans holding shares are pointless. Man Utd's biggest support groups are foreign anyway, and realistically couldn't give a monkeys who owns the club, much less who's in the starting eleven.