1. "He'd never beat Trump or Cruz in a general election."
Wrong. According to the latest polls, Bernie is the strongest Democratic candidate in the general election, defeating both Donald Trump and Ted Cruz in hypothetical matchups. (The latest Real Clear Politics averages of all polls shows Bernie beating Trump by a larger margin than Hillary beats Trump, and Bernie beating Cruz while Hillary loses to Cruz.)
2. "He couldn't get any of his ideas implemented because Congress would reject them."
If both house of Congress remain in Republican hands, no Democrat will be able to get much legislation through Congress, and will have to rely instead on executive orders and regulations. But there's a higher likelihood of kicking Republicans out if Bernie's "political revolution" continues to surge around America, bringing with it millions of young people and other voters, and keeping them politically engaged.
3. "America would never elect a socialist."
P-l-e-a-s-e. America's most successful and beloved government programs are social insurance - Social Security and Medicare. A highway is a shared social expenditure, as is the military and public parks and schools. The problem is we now have excessive socialism for the rich (bailouts of Wall Street, subsidies for Big Ag and Big Pharma, monopolization by cable companies and giant health insurers, giant tax-deductible CEO pay packages) - all of which Bernie wants to end or prevent.
4. "His single-payer healthcare proposal would cost so much it would require raising taxes on the middle class."
This is a duplicitous argument. Studies show that a single-payer system would be far cheaper than our current system, which relies on private for-profit health insurers, because a single-payer system wouldn't spend huge sums on advertising, marketing, executive pay, and billing. So even if the Sanders single-payer plan did require some higher taxes, Americans would come out way ahead because they'd save far more than that on health insurance.
5. "His plan for paying for college with a tax on Wall Street trades would mean colleges would run by government rules."
Baloney. Three-quarters of college students today already attend public universities financed largely by state governments, and they're not run by government rules. The real problem is too many young people still can't afford a college education. The move toward free public higher education that began in the 1950s with the G.I. Bill and extended into the 1960s came to an abrupt stop in the 1980s. We must restart it.
6. "He's too old."
Untrue. He's in great health. Have you seen how agile and forceful he is as he campaigns around the country? These days, 70s are the new 60s. (He's younger than four of the nine Supreme Court justices.) In any event, the issue isn't age; it's having the right values. FDR was paralyzed, and JFK had both Addison's and Crohn's diseases, but they were great presidents because they fought adamantly for social and economic justice.