You can tell when a topic gets really, really heated at San Jose City Hall, incandescent white in a world of gray.

A council member will put out a memo that attacks not only an opposing position, but the Mercury News, demanding that the council be given room to make its own decision.

That’s what happened over the weekend with Councilman Don Rocha, who has probably set the record for bristling and unpleasant memos in his four-years-plus on the council.

All of this has to do with a site that a lot of old-timers in San Jose know well — the block that includes plumbing contractor O.C. McDonald and Mel Cotton’s Sporting Goods on San Carlos Street.

A plan the City Council is scheduled to consider Tuesday could eventually allow for as many as 200 apartments on a 4.1-acre site on the south side of San Carlos between Lincoln Avenue and Race Street.

For that to happen, the city would have to convert the land’s designation from industrial/commercial to housing, a process discouraged by the city’s general plan.

This might sound dull to you. But there is very little the council does that is more important than land use. Essentially, the city is being asked to pawn one of its crown jewels.

A quick primer: O.C. McDonald and Mel Cotton’s provide jobs and sales tax, which the city desperately needs. An apartment project would provide new residents who would demand services like cops, libraries and parks.

Economically, it’s a loser for the city. You can trace a decline in the city’s finances — and hence, its ability to provide cops — to decisions made to convert land from industrial to residential purposes.

Domino effect

Where other cities, such as Santa Clara, have roughly 30 percent of its properties set aside for jobs, San Jose has only 15 percent.

“This has a potential domino effect,” says planning director Harry Freitas. “It would take money out of the city’s pocket, lose at least 100 jobs, and add probably another 400 residents.

Put another way, this is a very bad idea, even if you don’t shop at Mel Cotton’s (I have, over the years).

The politics of this makes it even more interesting. Under former Mayor Chuck Reed, conversions virtually stopped. But with five new council members, developers are trying again, despite opposition from new Mayor Sam Liccardo.

And for good reason: If the council should ultimately buckle and desert its general plan, it would suddenly increase the value of the land on San Carlos Street from $3.6 million to around $12 million for the owners.

That brings me back to Rocha, who seems to revel more in criticizing anti-conversion editorials and pointing out the alleged inconsistencies of his rivals than thinking very deeply about the city’s needs.

Rocha is arguing that the landowners and developers should have more time to process their request, which is what is on the table Tuesday.

But allowing that would give them another arrow in their quiver: They can argue they’ve put more money into the plan and should not be denied later on.

The best answer here is just to say no: O.C. McDonald and Mel Cotton’s are old-line businesses in San Jose, but they still employ people. This is the time for the council to stand with Liccardo and hold the line of the general plan.

Contact Scott Herhold at 408-275-0917 or sherhold@mercurynews.com. Twitter.com/scottherhold.